Theory and Modern Applications

# On the existence of solutions for a multi-singular pointwise defined fractional system

## Abstract

One of best ways for increasing our abilities in exact modeling of natural phenomena is working with a singular version of different fractional differential equations. As is well known, multi-singular equations are a modern version of singular equations. In this paper, we investigate the existence of solutions for a multi-singular fractional differential system. We consider some particular boundary value conditions on the system. By using the α-ψ-contractions and locating some control conditions, we prove that the system via infinite singular points has solutions. Finally, we provide an example to illustrate our main result.

## 1 Introduction

The fractional derivatives have an long history. It is natural that many phenomena could be modeled by using singular fractional integro-differential equations. Due to the emergence of fractional differential equations in some mathematical models of distinct phenomena in the world, fractional calculus is perfectly appealing ([112]) for some real modelings ([1315]). On the other side, much work is conducted in the field of fractional differential equations among which some have a singular point to control these sorts of points ([1619]) and we have nonlinear delay-fractional differential equations ([2023]).

In 2011, Feng et al. studied the existence of a solution for the singular system

$$\textstyle\begin{cases} D^{\alpha } u(t)+f(t, v(t))=0, \\ D^{\beta } v(t)+g(t, u(t))=0, \end{cases}$$

with boundary conditions $$u(0)=u(1)=u'(0)=v(0)=v(1)=v'(0)=0$$, where $$2< \alpha , \beta \leq 3$$, $$f,g: (0, \infty ) \times \mathbb{R} \rightarrow \mathbb{R}$$ are continuous, $$\lim_{t \rightarrow 0^{+}}f(t,\cdot)= +\infty$$ and $$\lim_{t \rightarrow 0^{+}}g(t,\cdot)= +\infty$$ ([24]). In 2014 Jleli et al. proved the existence of a positive solution for the singular fractional boundary value problem $$D^{\alpha } u(t)+ f(t, u(t))=0$$ with $$u(0) = u'(0) =0$$ and $$u'(1) = \sum_{i=1}^{m-2} \beta _{i} u'(\xi _{i})$$, where $$0 < t <1$$, $$2 < \alpha \leq 3$$, $$0 <\xi _{1} < \xi _{2}< \cdots< \xi _{m-2} < 1$$, $$f : (0,1] \times \mathbb{R} \to \mathbb{R}$$ is a continuous function, $$f(t, x)$$ is singular at $$t=0$$ and $$D^{\alpha }$$ is the Caputo derivative ([25]). Later, some more systems of fractional differential equations and inclusions were studied ([2628]). In 2017 Shabibi et al. reviewed the singular fractional integro-differential system

$$\textstyle\begin{cases} D^{\alpha _{1}} u_{1}+ f_{1}(t , u_{1} , \ldots , u_{m} , D^{\mu _{1}} u_{1}, \ldots , D^{\mu _{m}} u_{m} ) \\ \quad {}+g_{1}(t , u_{1} , \ldots , u_{m} , D^{\mu _{1}} u_{1}, \ldots , D^{ \mu _{m}} u_{m})=0, \\ \vdots \\ D^{\alpha _{m}} u_{m}+ f_{m}(t , u_{1} , \ldots , u_{m} , D^{\mu _{1}} u_{1}, \ldots , D^{\mu _{m}} u_{m} ) \\ \quad {}+ g_{m}(t , u_{1} , \ldots , u_{m} , D^{\mu _{1}} u_{1}, \ldots , D^{ \mu _{m}} u_{m})=0, \end{cases}$$

with boundary conditions $$u_{i}(0)=0$$, $$u_{i}'(1)=0$$ and $$\frac{d^{k}}{d t^{k}} [u_{i}(t)]_{t=0} = 0$$ for $$1 \leq i \leq m$$ and $$2 \leq k \leq n-1$$, where $$\alpha _{i} \geq 2$$, $$[\alpha _{i}]=n-1$$, $$0< \mu _{i} < 1$$, D is the Caputo fractional derivative, $$f_{i}$$ is a Caratheodory function, $$g_{i}$$ satisfies the Lipschitz condition and $$f_{i}(t ,x_{1}, \ldots , x_{2m})$$ is singular at $$t=0$$ of for all $$1 \leq i \leq m$$ ([29]). One of our aims is to generalize this system in a certain sense. In 2020, Talaee et al. studied the existence of solutions for the pointwise defined differential equation $$D^{\alpha } x(t) = f(t, x(t), x'(t), D^{\beta }x(t), \int _{0}^{t} g( \xi ) x(\xi ) \,d\xi )$$ with boundary conditions $$x(\mu )=\int _{0}^{1} h(z) x(z) \,dz$$ and $$x(0)= x^{(j)} (0) = 0$$, for $$2 \leq j\leq n-1$$, where $$\alpha \geq 2$$, $$n = [\alpha ] + 1$$, $$\mu , \beta \in (0,1)$$, $$g,h:[0,1] \to \mathbb{R}$$ are mappings such that $$g, h \in L^{1}[0,1]$$ and $$f\in L^{1}$$ is singular at some points of $$[0,1]$$ ([30]).

By using main idea of the literature, we investigate the existence of solutions for the nonlinear fractional differential pointwise defined system

\begin{aligned} \textstyle\begin{cases} D^{\alpha _{1}} x_{1}(t) = f_{1}(t, x_{1}(t), x'_{1}(t), D^{\beta _{1}}x_{1}(t), I^{p_{1}}x_{1}(t), \\ \hphantom{D^{\alpha _{1}} x_{1}(t) =}\ldots, x_{m}(t), x'_{m}(t), D^{\beta _{m}}x_{m}(t), I^{p_{m}}x_{m}(t)), \\ \vdots& \\ D^{\alpha _{m}} x_{m}(t) = f_{m}(t, x_{1}(t), x'_{1}(t), D^{\beta _{1}}x_{1}(t), I^{p_{1}}x_{1}(t), \\ \hphantom{D^{\alpha _{m}} x_{m}(t) =}\ldots, x_{m}(t), x'_{m}(t), D^{\beta _{m}}x_{m}(t), I^{p_{m}}x_{m}(t)), \end{cases}\displaystyle \quad t \in [0,1], \end{aligned}
(1)

with boundary value conditions $$x^{(j)}_{k}(0)= 0$$ for $$2 \leq j \leq n_{k} -1$$ and $$k= 1,\dots ,m$$,

$$x_{k}(\theta _{k})=\sum_{i=1}^{n_{0}} \lambda _{i,k} D^{\mu _{i,k} }x_{k}( \gamma _{i,k})$$

and $$x'_{k}(0)= x_{k}(\eta _{k})$$ for all $$k= 1,2, \ldots,m$$, where $$\lambda _{i,k} \geq 0$$, $$\beta _{k}, \gamma _{i,k}, \mu _{i,k}, \theta _{k}, \eta _{k} \in (0,1)$$, $$p_{k} >0$$, $$m, n_{0} \in \mathbb{N}$$, $$k= 1,2, \ldots,m$$, $$i= 1,2, \ldots,n_{0}$$, $$D^{\alpha _{k}}$$ is the Caputo fractional derivative of order $$\alpha _{k} \geq 2$$, $$n _{k}= [\alpha _{k}] + 1$$, $$f_{k} :[0,1] \times X ^{4m} \to \mathbb{R}$$, is singular at some points $$[0,1]$$, where $$X =C^{1}[0,1]$$. Note that in system (1), we investigate the problem with multi-singular points, while in the mentioned other systems, the problems have no singular points or have almost one singular point (in $$t=0$$). In fact, the novelty of this work is that the multi-singular points can be controlled and investigated. Note that system (1) is a generalization for the mentioned systems. Recall that $$D^{\alpha }x(t)=f(t)$$ is a pointwise defined equation on $$[0,1]$$ if there exists a set $$E \subset [0,1]$$ such that the measure of $$E^{c}$$ is zero and the equation holds on E ([30]). Recall that the Riemann–Liouville integral of order p with the lower limit $$a\geq 0$$ for a function $$f:(a,\infty )\to \mathbb{R}$$ is defined by $$I^{p}_{a^{+}}f(t)=\frac{1}{\Gamma (p)} \int _{a}^{t} (t-s)^{p-1} f(s)\,ds$$, provided that the right-hand side is pointwise defined on $$(a,\infty )$$. We denote $$I^{p}_{0^{+}}f(t)$$ by $$I^{p}f(t)$$ ([31]). The Caputo fractional derivative of order $$\alpha >0$$ is defined by $${}^{c}D^{ \alpha }f(t)=\frac{1}{\Gamma (n-\alpha )} \int _{0}^{t} \frac{f^{(n)}(s)}{(t-s)^{\alpha +1-n}}\,ds$$, where $$n=[\alpha ]+1$$ and $$f:(a,\infty )\to \mathbb{R}$$ is a function ([31]). Let Ψ be the family of nondecreasing functions $$\psi :[0,\infty ) \to [0,\infty )$$ such that $$\sum_{n=1}^{\infty } \psi ^{n}(t)<\infty$$ for all $$t> 0$$. One can check that $$\psi (t)< t$$ for all $$t>0$$ ([32]). Let $$T:X \to X$$ and $$\alpha :X \times X \to [0,\infty )$$ be two maps. Then T is called an α-admissible map whenever $$\alpha (x,y) \geq 1$$ implies $$\alpha (Tx,Ty) \geq 1$$ ([32]). Let $$(X,d)$$ be a metric space, $$\psi \in \Psi$$ and $$\alpha :X \times X \to [0,\infty )$$ a map. A self-map $$T:X \to X$$ is called an α-ψ-contraction whenever $$\alpha (x,y) d(Tx,Ty) \leq \psi (d(x,y))$$ for all $$x,y \in X$$ ([32]). We need the following results.

### Lemma 1.1

([32])

Let $$(X,d)$$ be a complete metric space, $$\psi \in \Psi$$, $$\alpha :X \times X \to [0,\infty )$$ a map and $$T:X \to X$$ an α-admissible α-ψ-contraction. If T is continuous and there exists $$x_{0} \in X$$ such that $$\alpha (x_{0}, Tx_{0}) \geq 1$$, then T has a fixed point.

### Lemma 1.2

([33])

Let $$n-1\leq \alpha < n$$ and $$x\in C(0,1)$$. Then $$I^{\alpha } D^{\alpha }x(t)=x(t)+ \sum_{i=0}^{n-1} c_{i}t^{i}$$ for some real constants $$c_{0},\dots ,c_{n-1}$$.

## 2 Main results

Now, we present our main results.

### Lemma 2.1

Let $$\alpha \geq 2$$, $$[\alpha ] =n-1$$, $$\lambda _{i} \geq 0$$, $$\mu _{i} , \gamma _{i}, \eta \in (0,1)$$ for all $$i=1, \ldots, n_{0}$$, $$\theta \in (0,1)$$ and $$f\in L^{1} [0,1]$$. Then the solution of the problem $$D^{\alpha } x(t)=f(t)$$ with the boundary conditions $$x^{(j)}(0)= 0$$ for $$2 \leq j \leq n -1$$, $$x(\theta )=\sum_{i=1}^{n_{0}} \lambda _{i} D^{\mu _{i} }x(\gamma _{i})$$ and $$x'(0)= x(\eta )$$ is given by

\begin{aligned} x(t) =& \frac{1}{\Gamma (\alpha )} \int ^{t}_{0} (t-s)^{\alpha - 1} f(s) \,ds \\ &{} + \frac{1 - \eta + t}{(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\theta }_{0} (\theta -s)^{\alpha - 1} f(s) \,ds \\ &{}- \frac{1 - \eta + t }{(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{\alpha - 1} f(s) \,ds \\ & {}-\frac{1 - \eta +t}{(\Delta _{\gamma } - \theta - 1 +\eta )} \sum_{i=1}^{n_{0}} \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds, \end{aligned}

where $$\Delta _{\gamma } := \sum_{i=1}^{n_{0}} \frac{\lambda _{i} (\gamma _{i})^{1- \mu _{i}}}{\Gamma (2 -\mu _{i})}$$ and $$1- \Delta _{\gamma } \neq \eta - \theta$$.

### Proof

By using a similar method to [30], we conclude that Lemma 1.2 holds on $$L^{1}[0,1]$$. Let x be a solution for the problem. By using Lemma 1.2, we have

\begin{aligned} x(t)= \frac{1}{\Gamma (\alpha )} \int ^{t}_{0} (t-s)^{\alpha - 1} f(s) \,ds +c_{0} + c_{1} t + \cdots + c_{n-1} t^{n-1}. \end{aligned}

Since $$x^{(j)}(0)= 0$$ for $$2 \leq j \leq n -1$$, we conclude that

\begin{aligned} x(t)= \frac{1}{\Gamma (\alpha )} \int ^{t}_{0} (t-s)^{\alpha - 1} f(s) \,ds +c_{0} + c_{1} t \end{aligned}
(2)

and so $$x(\eta )= \frac{1}{\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{ \alpha - 1} f(s) \,ds +c_{0} + c_{1} \eta$$ and $$x'(t)= \frac{1}{\Gamma (\alpha -1)} \int ^{t}_{0} (t-s)^{\alpha - 2} f(s) \,ds +c_{1}$$. Thus, $$x'(0) = c_{1}$$ and by using the boundary condition $$x'(0) =x(\eta )$$ we get

\begin{aligned} \frac{1}{\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{\alpha - 1} f(s) \,ds +c_{0} + c_{1} \eta = c_{1}. \end{aligned}

Hence,

\begin{aligned} c_{1} = \frac{1}{(1- \eta )\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{ \alpha - 1} f(s) \,ds + \frac{1}{1- \eta }c_{0}. \end{aligned}
(3)

On the other hand by using (2), for each $$i= 1, \ldots, n_{0}$$ we have

\begin{aligned} D^{\mu _{i}} x(t)= \frac{1}{\Gamma (\alpha -\mu _{i})} \int ^{t}_{0} (t-s)^{ \alpha - \mu _{i} -1} f(s) \,ds +c_{1} \frac{t^{1- \mu _{i}}}{\Gamma (2 -\mu _{i})} \end{aligned}

which implies $$\lambda _{i} D^{\mu _{i}} x(\gamma _{i})= \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds +c_{1} \frac{\lambda _{i} (\gamma _{i})^{1- \mu _{i}}}{\Gamma (2 -\mu _{i})}$$. Hence,

\begin{aligned} \sum_{i=1}^{n_{0}} \lambda _{i} D^{\mu _{i}} x(\gamma _{i})= \sum_{i=1}^{n_{0}} \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds +c_{1} \sum_{i=1}^{n_{0}} \frac{\lambda _{i} (\gamma _{i})^{1- \mu _{i}}}{\Gamma (2 -\mu _{i})}. \end{aligned}

Since $$x(\theta )= \frac{1}{\Gamma (\alpha )} \int ^{\theta }_{0} (\theta -s)^{ \alpha - 1} f(s) \,ds +c_{0} + c_{1} \theta$$ and $$x(\theta ) = \sum_{i=1}^{n_{0}} \lambda _{i} D^{\mu _{i}} x(\gamma _{i})$$, we obtain

\begin{aligned}& \frac{1}{\Gamma (\alpha )} \int ^{\theta }_{0} (\theta -s)^{ \alpha - 1} f(s) \,ds +c_{0} + c_{1} \theta \\& \quad = \sum_{i=1}^{n_{0}} \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds +c_{1} \sum_{i=1}^{n_{0}} \frac{\lambda _{i} (\gamma _{i})^{1- \mu _{i}}}{\Gamma (2 -\mu _{i})} \end{aligned}

and so by using (3), we have

\begin{aligned}& \frac{1}{\Gamma (\alpha )} \int ^{\theta }_{0} (\theta -s)^{ \alpha - 1} f(s) \,ds +c_{0} + \frac{\theta }{(1- \eta )\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{ \alpha - 1} f(s) \,ds \\& \quad {} + \frac{\theta }{1- \eta }c_{0} = \sum _{i=1}^{n_{0}} \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds \\& \quad {}+ \frac{ \sum_{i=1}^{n_{0}} \frac{\lambda _{i} (\gamma _{i})^{1- \mu _{i}}}{\Gamma (2 -\mu _{i})}}{(1- \eta )\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{\alpha - 1} f(s) \,ds + \frac{ \sum_{i=1}^{n_{0}} \frac{\lambda _{i} (\gamma _{i})^{1- \mu _{i}}}{\Gamma (2 -\mu _{i})}}{1- \eta }c_{0}. \end{aligned}

If $$\Delta _{\gamma } := \sum_{i=1}^{n_{0}} \frac{\lambda _{i} (\gamma _{i})^{1- \mu _{i}}}{\Gamma (2 -\mu _{i})}$$, then

\begin{aligned} c_{0} \biggl(\frac{ \Delta _{\gamma } - \theta - 1 +\eta }{1 - \eta } \biggr) =& \frac{1}{\Gamma (\alpha )} \int ^{\theta }_{0} (\theta -s)^{ \alpha - 1} f(s) \,ds \\ &{} + \frac{\theta }{(1- \eta )\Gamma (\alpha )} \int ^{\eta }_{0} ( \eta -s)^{\alpha - 1} f(s) \,ds \\ &{} - \sum_{i=1}^{n_{0}} \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds \\ &{}-\frac{ \Delta _{\gamma }}{(1- \eta )\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{\alpha - 1} f(s) \,ds \end{aligned}

so

\begin{aligned} c_{0} =& \frac{1 - \eta }{(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\theta }_{0} (\theta -s)^{\alpha - 1} f(s) \,ds \\ &{} -\frac{1 - \eta }{(\Delta _{\gamma } - \theta - 1 +\eta )} \sum_{i=1}^{n_{0}} \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds \\ &{}+ \frac{\theta - \Delta _{\gamma }}{(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{\alpha - 1} f(s) \,ds. \end{aligned}

Thus, by using (2) and (3) we get

\begin{aligned} c_{1} =& \frac{1}{(1 - \eta )\Gamma (\alpha )} \int ^{ \eta }_{0} ( \eta -s)^{\alpha - 1} f(s) \,ds \\ &{} + \frac{1}{(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\theta }_{0} (\theta -s)^{\alpha - 1} f(s) \,ds \\ &{}+ \frac{\theta - \Delta _{\gamma }}{(\Delta _{\gamma } - \theta - 1 +\eta )(1 - \eta )\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{\alpha - 1} f(s) \,ds \\ & {}-\frac{1}{(\Delta _{\gamma } - \theta - 1 +\eta )} \sum_{i=1}^{n_{0}} \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds \end{aligned}

and

\begin{aligned} x(t) =& \frac{1}{\Gamma (\alpha )} \int ^{t}_{0} (t-s)^{\alpha - 1} f(s) \,ds \\ &{} + \frac{1 - \eta }{(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\theta }_{0} (\theta -s)^{\alpha - 1} f(s) \,ds \\ &{}+ \frac{\theta - \Delta _{\gamma }}{(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{\alpha - 1} f(s) \,ds \\ & {}-\frac{1 - \eta }{(\Delta _{\gamma } - \theta - 1 +\eta )} \sum_{i=1}^{n_{0}} \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds \\ &{}+ \frac{t}{(1 - \eta )\Gamma (\alpha )} \int ^{ \eta }_{0} ( \eta -s)^{ \alpha - 1} f(s) \,ds \\ & {}+ \frac{t}{(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\theta }_{0} (\theta -s)^{\alpha - 1} f(s) \,ds \\ &{}+ \frac{(\theta - \Delta _{\gamma })t}{(\Delta _{\gamma } - \theta - 1 +\eta )(1 - \eta )\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{\alpha - 1} f(s) \,ds \\ & {}-\frac{t}{(\Delta _{\gamma } - \theta - 1 +\eta )} \sum_{i=1}^{n_{0}} \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds. \end{aligned}

Hence,

\begin{aligned} x(t) =& \frac{1}{\Gamma (\alpha )} \int ^{t}_{0} (t-s)^{\alpha - 1} f(s) \,ds \\ & {}+ \frac{1 - \eta + t}{(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\theta }_{0} (\theta -s)^{\alpha - 1} f(s) \,ds \\ &{}+ \frac{-(1 - \eta )^{2} +(\theta - \Delta _{\gamma })t + t (\Delta _{\gamma } - \theta - 1 +\eta )}{(1 - \eta )(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{\alpha - 1} f(s) \,ds \\ &{} -\frac{1 - \eta +t}{(\Delta _{\gamma } - \theta - 1 +\eta )} \sum_{i=1}^{n_{0}} \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds \end{aligned}

and so

\begin{aligned} x(t) =& \frac{1}{\Gamma (\alpha )} \int ^{t}_{0} (t-s)^{\alpha - 1} f(s) \,ds \\ & {}+ \frac{1 - \eta + t}{(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\theta }_{0} (\theta -s)^{\alpha - 1} f(s) \,ds \\ &{}- \frac{1 - \eta + t }{(\Delta _{\gamma } - \theta - 1 +\eta )\Gamma (\alpha )} \int ^{\eta }_{0} (\eta -s)^{\alpha - 1} f(s) \,ds \\ &{} -\frac{1 - \eta +t}{(\Delta _{\gamma } - \theta - 1 +\eta )} \sum_{i=1}^{n_{0}} \frac{\lambda _{i}}{\Gamma (\alpha -\mu _{i})} \int ^{\gamma _{i}}_{0} (\gamma _{i} -s)^{\alpha - \mu _{i} -1} f(s) \,ds. \end{aligned}

This completes the proof. □

Consider the space $$X= C^{1}[0,1]$$ with the norm $$\| \cdot \|_{*}$$ and the space $$X^{m}$$ with the norm $$\| \cdot \|_{**}$$, where $$\|(x_{1},\ldots,x_{m})\|_{**} = \max \{ \|x_{1}\|_{*},\ldots, \|x_{m}\|_{*} \}$$, $$\|x\|_{*} = \max \{ \|x\|, \|x'\| \}$$ and $$\| . \|$$ is the supremum norm on $$C[0,1]$$. Let $$f_{k}$$ be a map $$[0,1]\times X^{4m}$$ that is singular at some points of $$[0,1]$$, for $$k=1, \ldots, m$$. Define $$F:X^{m} \to X^{m}$$ as

$$F(x_{1},\ldots,x_{m}) (t) = \begin{pmatrix} \phi _{1}(x_{1},\ldots,x_{m})(t) \\ \vdots \\ \phi _{m}(x_{1},\ldots,x_{m})(t) \end{pmatrix} ,$$

where

\begin{aligned} &\phi _{k}(x_{1},\ldots,x_{m}) (t) \\ &\quad = \frac{1}{\Gamma (\alpha _{k})} \int ^{t}_{0} (t-s)^{\alpha _{k} - 1} f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\ &\qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \,ds \\ &\qquad {} + \frac{1 - \eta _{k} + t}{(\Delta _{\gamma } - \theta _{k} - 1 +\eta )\Gamma (\alpha )} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\ &\qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \,ds \\ &\qquad {}- \frac{1 - \eta _{k} + t }{(\Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k})\Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\ &\qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \,ds \\ &\qquad {} - \frac{1 - \eta _{k} +t}{(\Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k})} \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} f_{k} \bigl(s, x_{1}(s), x'_{1}(s), \\ &\qquad D^{\beta _{1}}x_{1}(s), I^{p_{1}}x_{1}(s), \ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \,ds, \end{aligned}

for $$1 \leq k \leq m$$, where $$\Delta _{\gamma _{k}} := \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k} (\gamma _{i,k})^{1- \mu _{i,k}}}{\Gamma (2 -\mu _{i,k})}$$. Then we have

$$F'(x_{1},\ldots,x_{m}) (t) = \begin{pmatrix} \phi '_{1}(x_{1},\ldots,x_{m})(t) \\ \vdots \\ \phi '_{m}(x_{1},\ldots,x_{m})(t) \end{pmatrix} ,$$

where for each $$1 \leq k \leq m$$ we have

\begin{aligned} &\phi '_{k}(x_{1},\ldots,x_{m}) (t) \\ &\quad = \frac{1}{\Gamma (\alpha _{k} - 1)} \int ^{t}_{0} (t-s)^{\alpha _{k} - 2} f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\ & \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \,ds \\ & \qquad {}+ \frac{1}{(\Delta _{\gamma } - \theta _{k} - 1 +\eta )\Gamma (\alpha )} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\ & \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \,ds \\ & \qquad {}- \frac{1 }{(\Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k})\Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\ & \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \,ds \\ & \qquad {} -\frac{1 }{(\Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k})} \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} f_{k} \bigl(s, x_{1}(s), x'_{1}(s), \\ & \qquad D^{\beta _{1}}x_{1}(s), I^{p_{1}}x_{1}(s), \ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \,ds. \end{aligned}

It is obvious that the singular pointwise defined equation (1) has a solution u if and only if u is a fixed point of the map F.

### Theorem 2.2

Let m, n and $$n_{0}$$ be natural numbers, $$\alpha _{k} \geq 2$$, $$[\alpha _{k}] =n_{k}-1$$, $$\lambda _{i,k} \geq 0$$, $$\gamma _{i,k}, \mu _{i,k}, \theta _{k}, \eta _{k} \in (0,1)$$, $$p_{k} >0$$ for $$i=1,\ldots,n_{0}$$ and $$k=1,2,\ldots,m$$, $$f_{k}: [0, 1] \times X^{m} \to \mathbb{R}$$ some singular mappings on some points of $$[0, 1]$$ such that

$$\bigl\vert f_{k}(t, x_{1}, \ldots, x_{4m}) - f_{k}(t, y_{1}, \ldots, y_{4m}) \bigr\vert \leq \Phi _{k}(t) M_{k} \bigl( \vert x_{1} - y_{1} \vert , \ldots, \vert x_{4m} - y_{4m} \vert \bigr)$$

for all $$x_{1}, \ldots, x_{4m}, y_{1}, \ldots, y_{4m} \in X$$ and almost all $$t \in [0,1]$$. Assume that

$$\bigl\vert f_{i}(t, x_{1}, \ldots, x_{4m}) \bigr\vert \leq \sum_{j=1}^{4m} T_{k,j} \bigl(t, \vert x_{k} \vert \bigr),$$

where $$M_{k} :X^{4m} \to \mathbb{R}^{+}$$ is non-decreasing mapping respect to all components such that $$\lim_{z \to 0^{+}} \frac{M_{k}(z,\ldots,z)}{z} :=q_{k} \in [0,\infty )$$ and $$T_{k,j} : [0, 1] \times X \to \mathbb{R}^{+}$$ is a map with $$T_{k,j}(\cdot,z)$$ is nondecreasing respect to z and $$\lim_{z \to 0^{+}} \frac{T_{k,j}(t,z)}{z} :=b_{k,j}(t)$$ for almost all $$t \in [0,1]$$ and for some $$b_{k,j}: \in \mathbb{R}^{+}[0,1] \to \mathbb{R^{+}}$$ such that $$(1-t)^{\alpha _{k} -2}b_{k,j}(t) \in L^{1}[0,1]$$ for $$1 \leq j \leq 4m$$ and $$1 \leq {k \leq m}$$. Let $$\Delta = \max \{ 1, \frac{1}{\Gamma (2- \beta _{1})}, \ldots, \frac{1}{\Gamma (2- \beta _{m})},\frac{1}{\Gamma (p_{1} +1)}, \ldots, \frac{1}{\Gamma (p_{m} +1)} \}$$ and $$\hat{ b}_{i,k}, \hat{\phi }_{k} \in L^{1}[0,1]$$, $$\Delta _{\gamma _{k}} := \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k} (\gamma _{i,k})^{1- \mu _{i,k}}}{\Gamma (2 -\mu _{i,k})}$$ and $$1- \Delta _{\gamma _{k}} \neq \eta _{k} - \theta _{k}$$, where $$\hat{\phi }_{k}(s) = (1-s)^{\alpha _{i} -2} a_{i,j}(s)$$. If

\begin{aligned}& \max_{1 \leq k \leq m} \Biggl[ \frac{1 }{\Gamma (\alpha _{k} -1)} + \frac{2(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \quad {}+ \frac{(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \max \Biggl\{ \sum _{j=1}^{m} \Vert \hat{b}_{k,j} \Vert , q_{k} \hat{\Phi }_{k} \Biggr\} \in \biggl[0, \frac{1}{\Delta } \biggr), \end{aligned}

then the pointwise defined system

\begin{aligned} \textstyle\begin{cases} D^{\alpha _{1}} x_{1}(t) = f_{1}(t, x_{1}(t), x'_{1}(t), D^{\beta _{1}}x_{1}(t), I^{p_{1}}x_{1}(t), \\ \hphantom{D^{\alpha _{1}} x_{1}(t) =}\ldots, x_{m}(t), x'_{m}(t), D^{\beta _{m}}x_{m}(t), I^{p_{m}}x_{m}(t)), \\ D^{\alpha _{m}} x_{m}(t) + f_{m}(t, x_{1}(t), x'_{1}(t), D^{\beta _{1}}x_{1}(t), I^{p_{1}}x_{1}(t), \\ \quad \ldots, x_{m}(t), x'_{m}(t), D^{\beta _{m}}x_{m}(t), I^{p_{m}}x_{m}(t)), \end{cases}\displaystyle \end{aligned}

with boundary conditions $$x^{(j)}_{k}(0)= 0$$, $$x_{k}(\theta _{k})=\sum_{i=1}^{n_{0}} \lambda _{i,k} D^{\mu _{i,k} }x_{k}( \gamma _{i,k})$$ and $$x'_{k}(0)= x_{k}(\eta _{k})$$ for $$2 \leq j \leq n_{k}-1$$ and $$1\leq k\leq m$$, has a solution.

### Proof

First, we prove F is continuous on $$X^{m}$$. Let $$\epsilon >0$$ and $$\|(x_{1},\ldots,x_{m}) - (y_{1},\ldots,y_{m})\|_{**} < \epsilon$$. Then $$\max_{1 \leq k \leq m} \|x_{k} - y_{k} \|_{*} < \epsilon$$ and so $$\|x_{k} - y_{k} \|_{*} < \epsilon$$ for all $$1 \leq k \leq m$$. Thus,

\begin{aligned}& \bigl\vert \phi _{k}(x_{1},\ldots, x_{n}) (t)-\phi _{k}(y_{1},\ldots, y_{n}) (t) \bigr\vert \\& \quad \leq \frac{1}{\Gamma (\alpha _{k})} \int ^{t}_{0} (t-s)^{\alpha _{k} - 1} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) - f_{k} \bigl(s, y_{1}(s), y'_{1}(s), \\& \qquad D^{\beta _{1}}y_{1}(s), I^{p_{1}}y_{1}(s), \ldots, y_{m}(s), y'_{m}(s), D^{\beta _{m}}y_{m}(s), I^{p_{m}}y_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {} + \frac{1 - \eta _{k} + t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) - f_{k} \bigl(s, y_{1}(s), y'_{1}(s), \\& \qquad D^{\beta _{1}}y_{1}(s), I^{p_{1}}y_{1}(s), \ldots, y_{m}(s), y'_{m}(s), D^{\beta _{m}}y_{m}(s), I^{p_{m}}y_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) - f_{k} \bigl(s, y_{1}(s), y'_{1}(s), \\& \qquad D^{\beta _{1}}y_{1}(s), I^{p_{1}}y_{1}(s), \ldots, y_{m}(s), y'_{m}(s), D^{\beta _{m}}y_{m}(s), I^{p_{m}}y_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {} + \frac{1 - \eta _{k} +t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {}\times \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), \\& \qquad I^{p_{m}}x_{m}(s) \bigr) - f_{k} \bigl(s, y_{1}(s), y'_{1}(s), D^{\beta _{1}}y_{1}(s), I^{p_{1}}y_{1}(s), \\& \qquad \ldots, y_{m}(s), y'_{m}(s), D^{\beta _{m}}y_{m}(s), I^{p_{m}}y_{m}(s) \bigr) \bigr\vert \,ds \\& \quad \leq \frac{1}{\Gamma (\alpha _{k})} \int ^{t}_{0} (t-s)^{\alpha _{k} - 1} \Phi _{k}(s) M_{k} \bigl( \bigl\vert x_{1}(s) - y_{1}(s) \bigr\vert , \bigl\vert x'_{1}(s) - y'_{1}(s) \bigr\vert , \\& \qquad \bigl\vert D^{\beta _{1}}(x_{1}- y_{1}) (s) \bigr\vert , I^{p_{1}}(x_{1} - y_{1}) (s) \vert , \ldots, \bigl\vert x_{m}(s) - y_{m}(s) \bigr\vert , \\& \qquad \bigl\vert x'_{m}(s) - y'_{m}(s) \bigr\vert , \bigl\vert D^{\beta _{m}}(x_{m}- y_{m}) (s) \bigr\vert , I^{p_{m}}(x_{m} - y_{m}) (s) \vert \bigr) \,ds \\& \qquad {} + \frac{1 - \eta _{k} + t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \Phi _{k}(s) M_{k} \bigl( \bigl\vert x_{1}(s) - y_{1}(s) \bigr\vert , \bigl\vert x'_{1}(s) - y'_{1}(s) \bigr\vert , \\& \qquad \bigl\vert D^{\beta _{1}}(x_{1}- y_{1}) (s) \bigr\vert , I^{p_{1}}(x_{1} - y_{1}) (s) \vert , \ldots, \bigl\vert x_{m}(s) - y_{m}(s) \bigr\vert , \\& \qquad \bigl\vert x'_{m}(s) - y'_{m}(s) \bigr\vert , \bigl\vert D^{\beta _{m}}(x_{m}- y_{m}) (s) \bigr\vert , I^{p_{m}}(x_{m} - y_{m}) (s) \vert \bigr) \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1}\Phi _{k}(s) M_{k} \bigl( \bigl\vert x_{1}(s) - y_{1}(s) \bigr\vert , \bigl\vert x'_{1}(s) - y'_{1}(s) \bigr\vert , \\& \qquad \bigl\vert D^{\beta _{1}}(x_{1}- y_{1}) (s) \bigr\vert , I^{p_{1}}(x_{1} - y_{1}) (s) \vert , \ldots, \bigl\vert x_{m}(s) - y_{m}(s) \bigr\vert , \\& \qquad \bigl\vert x'_{m}(s) - y'_{m}(s) \bigr\vert , \bigl\vert D^{\beta _{m}}(x_{m}- y_{m}) (s) \bigr\vert , I^{p_{m}}(x_{m} - y_{m}) (s) \vert \bigr) \,ds \\& \qquad {}+ \frac{1 - \eta _{k} +t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {}\times \Phi _{k}(s) M_{k} \bigl( \bigl\vert x_{1}(s) - y_{1}(s) \bigr\vert , \bigl\vert x'_{1}(s) - y'_{1}(s) \bigr\vert , \bigl\vert D^{\beta _{1}}(x_{1}- y_{1}) (s) \bigr\vert , I^{p_{1}}(x_{1} - y_{1}) (s) \vert , \\& \qquad\ldots, \bigl\vert x_{m}(s) - y_{m}(s) \bigr\vert , \bigl\vert x'_{m}(s) - y'_{m}(s) \bigr\vert , \bigl\vert D^{\beta _{m}}(x_{m}- y_{m}) (s) \bigr\vert , I^{p_{m}}(x_{m} - y_{m}) (s) \vert \bigr) \,ds \end{aligned}

for all $$1 \leq k \leq m$$ and $$t \in [0,1]$$. Now for $$\beta \in (0,1)$$ and $$t \in [0,1]$$, we have

$$D^{\beta }( x-y) (t)=\frac{1}{\Gamma (1- \beta )} \int _{0}^{t} (t-s)^{ \beta -2} \bigl(x' - y' \bigr) (s) \,ds$$

and so $$|D^{\beta } (x-y)(t)|\leq \frac{\|x' -y'\|}{\Gamma (1- \beta )} \int _{0}^{t} (t-s)^{\beta -2} \,ds = \frac{\|x' -y'\|}{\Gamma (2- \beta )} t^{\beta -1}$$. Hence, $$|D^{\beta } (x-y)(t)|\leq \frac{\|x' -y'\|}{\Gamma (2- \beta )}$$ and $$|I^{p} (x-y)(t)|\leq \frac{\|x -y\|}{\Gamma (p)} \int _{0}^{t} (t-s)^{p-1} \,ds = \frac{\|x -y\|}{\Gamma (p +1)} t^{p}$$. Thus, $$|I^{p} (x-y)(t)|\leq \frac{\|x -y\|}{\Gamma (p +1)}$$ and

\begin{aligned}& \bigl\vert \phi _{k}(x_{1},\ldots, x_{n}) (t)-\phi _{k}(y_{1},\ldots, y_{n}) (t) \bigr\vert \\& \quad \leq \frac{1}{\Gamma (\alpha _{k})} \int ^{t}_{0} (t-s)^{\alpha _{k} - 1} \Phi _{k}(s) M_{k} \biggl( \Vert x_{1} - y_{1} \Vert , \bigl\Vert x'_{1} - y'_{1} \bigr\Vert , \frac{ \Vert x'_{1} -y'_{1} \Vert }{\Gamma (2- \beta _{1})}, \\& \qquad \frac{ \Vert x_{1} -y_{1} \Vert }{\Gamma (p_{1} +1)},\ldots, \Vert x_{m} - y_{m} \Vert , \bigl\Vert x'_{m} - y'_{m} \bigr\Vert , \frac{ \Vert x'_{m} -y'_{m} \Vert }{\Gamma (2- \beta _{m})}, \frac{ \Vert x_{m} -y_{m} \Vert }{\Gamma (p_{m} +1)} \biggr) \,ds \\& \qquad {} + \frac{1 - \eta _{k} + t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \Phi _{k}(s) M_{k} \biggl( \Vert x_{1} - y_{1} \Vert , \bigl\Vert x'_{1} - y'_{1} \bigr\Vert , \\& \qquad \frac{ \Vert x'_{1} -y'_{1} \Vert }{\Gamma (2- \beta _{1})}, \frac{ \Vert x_{1} -y_{1} \Vert }{\Gamma (p_{1} +1)},\ldots, \Vert x_{m} - y_{m} \Vert , \bigl\Vert x'_{m} - y'_{m} \bigr\Vert , \frac{ \Vert x'_{m} -y'_{m} \Vert }{\Gamma (2- \beta _{m})}, \frac{ \Vert x_{m} -y_{m} \Vert }{\Gamma (p_{m} +1)} \biggr) \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1}\Phi _{k}(s) M_{k} \biggl( \Vert x_{1} - y_{1} \Vert , \bigl\Vert x'_{1} - y'_{1} \bigr\Vert , \\& \qquad \frac{ \Vert x'_{1} -y'_{1} \Vert }{\Gamma (2- \beta _{1})}, \frac{ \Vert x_{1} -y_{1} \Vert }{\Gamma (p_{1} +1)},\ldots, \Vert x_{m} - y_{m} \Vert , \bigl\Vert x'_{m} - y'_{m} \bigr\Vert , \frac{ \Vert x'_{m} -y'_{m} \Vert }{\Gamma (2- \beta _{m})}, \frac{ \Vert x_{m} -y_{m} \Vert }{\Gamma (p_{m} +1)} \biggr) \,ds \\& \qquad {}+ \frac{1 - \eta _{k} +t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {}\times \Phi _{k}(s)M_{k} \biggl( \Vert x_{1} - y_{1} \Vert , \bigl\Vert x'_{1} - y'_{1} \bigr\Vert , \frac{ \Vert x'_{1} -y'_{1} \Vert }{\Gamma (2- \beta _{1})}, \frac{ \Vert x_{1} -y_{1} \Vert }{\Gamma (p_{1} +1)},\ldots, \\& \qquad \Vert x_{m} - y_{m} \Vert , \bigl\Vert x'_{m} - y'_{m} \bigr\Vert , \frac{ \Vert x'_{m} -y'_{m} \Vert }{\Gamma (2- \beta _{m})}, \frac{ \Vert x_{m} -y_{m} \Vert }{\Gamma (p_{m} +1)} \biggr) \,ds \\& \quad \leq \frac{1}{\Gamma (\alpha _{k})} \int ^{t}_{0} (t-s)^{\alpha _{k} - 1} \Phi _{k}(s) M_{k} \bigl( \Delta _{1} \Vert x_{1} - y_{1} \Vert _{*}, \ldots, \Delta _{1} \Vert x_{1} - y_{1} \Vert _{*}, \\& \qquad \ldots, \Delta _{m} \Vert x_{m} - y_{m} \Vert _{*},\ldots, \Delta _{m} \Vert x_{m} - y_{m} \Vert _{*}, \bigr) \,ds \\& \qquad {} + \frac{1 - \eta _{k} + t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \Phi _{k}(s)M_{k} \bigl( \Delta _{1} \Vert x_{1} - y_{1} \Vert _{*}, \\& \qquad \ldots, \Delta _{1} \Vert x_{1} - y_{1} \Vert _{*},\ldots, \Delta _{m} \Vert x_{m} - y_{m} \Vert _{*},\ldots, \Delta _{m} \Vert x_{m} - y_{m} \Vert _{*} \bigr) \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1}\Phi _{k}(s) M_{k} \bigl( \Delta _{1} \Vert x_{1} - y_{1} \Vert _{*}, \\& \qquad \ldots, \Delta _{1} \Vert x_{1} - y_{1} \Vert _{*},\ldots, \Delta _{m} \Vert x_{m} - y_{m} \Vert _{*},\ldots, \Delta _{m} \Vert x_{m} - y_{m} \Vert _{*} \bigr) \,ds \\& \qquad {} + \frac{1 - \eta _{k} +t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {}\times \Phi _{k}(s) M_{k} \bigl( \Delta _{1} \Vert x_{1} - y_{1} \Vert _{*}, \ldots, \Delta _{1} \Vert x_{1} - y_{1} \Vert _{*}, \\& \qquad \ldots, \Delta _{m} \Vert x_{m} - y_{m} \Vert _{*},\ldots, \Delta _{m} \Vert x_{m} - y_{m} \Vert _{*} \bigr) \,ds, \end{aligned}

where for $$1 \leq j \leq m$$ $$\Delta _{j} = \max \{ 1, \frac{1}{\Gamma (2 - \beta _{j})}, \frac{1}{\Gamma (p_{j} + 1)} \}$$ and $$\|x_{j} - y_{j}\|_{*} = \max \{ \|x_{j} - y_{j}\|, \|x'_{j} - y'_{j} \| \}$$. Let $$\Delta = \max_{1 \leq j \leq m} \Delta _{j}$$ and $$\|(x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n})\|_{**} = \max_{1 \leq j \leq m} \{ \|x_{j} - y_{j}\|_{*} \}$$. Then, for each $$t \in [0,1]$$ and $$1 \leq j \leq m$$, we have

\begin{aligned}& \bigl\vert \phi _{k}(x_{1},\ldots, x_{n}) (t)-\phi _{k}(y_{1},\ldots, y_{n}) (t) \bigr\vert \\& \quad \leq \frac{ M_{k} ( \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**},\ldots, \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**})}{\Gamma (\alpha _{k})} \\& \qquad {} \times \int ^{1}_{0} (1-s)^{\alpha _{k} - 1} \Phi _{k}(s) \,ds \\& \qquad {} + (1 - \eta _{k} + t ) M_{k} \bigl( \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**},\ldots, \\& \qquad \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**}\bigr)/ \bigl( \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})\bigr) \\& \qquad {}\times \int ^{1}_{0} (1 -s)^{\alpha _{k} - 1} \Phi _{k}(s) \,ds \\& \qquad {} + (1 - \eta _{k} + t ) M_{k} \bigl( \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**},\ldots, \\& \qquad \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**}\bigr)/ \bigl( \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})\bigr) \\& \qquad {}\times \int ^{1}_{0} (1 -s)^{\alpha - 1}\Phi _{k}(s) \,ds \\& \qquad {}+ (1 - \eta _{k} + t ) M_{k} \bigl( \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**},\ldots, \\& \qquad {}\Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**}\bigr)/ \bigl( \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \bigr) \\& \qquad {}\times \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{1}_{0} (1 -s)^{\alpha _{k} - \mu _{i,k} -1} \Phi _{k}(s) \,ds. \end{aligned}
(4)

Since $$\lim_{z \to 0^{+}} \frac{M_{k}(\Delta z,\ldots, \Delta z)}{\Delta z}= q_{k}$$, for each $$\epsilon >0$$ there exists $$\delta (\epsilon )> 0$$ such that $$0 < z < \delta (\epsilon )$$ implies $$\frac{M_{k}(\Delta z,\ldots, \Delta z)}{\Delta z} < q_{k} + \epsilon$$ for all $$1 \leq k \leq m$$. Thus,

\begin{aligned} M_{k}(\Delta z,\ldots, \Delta z) < (q_{k} + \epsilon ) \Delta z \end{aligned}
(5)

for $$0 < z < \delta (\epsilon )$$. Put $$\delta _{M}(\epsilon ) = \min \{\delta (\epsilon ), \epsilon \}$$. Then, for each $$0 < z < \delta _{M}(\epsilon )$$, we have

$$M_{k}(\Delta z,\ldots, \Delta z) < (q_{k} + \epsilon ) \Delta \epsilon$$

for all $$1 \leq k \leq m$$. Let $$\|(x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n})\|_{**} < \delta _{M}( \epsilon )$$. Then we have

$$M_{k} \bigl(\Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**},\ldots, \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**} \bigr) < (q_{k} + \epsilon ) \Delta \epsilon$$

for all $$1 \leq k \leq m$$ and so

\begin{aligned}& \bigl\vert \phi _{k}(x_{1},\ldots, x_{n}) (t)-\phi _{k}(y_{1},\ldots, y_{n}) (t) \bigr\vert \\& \quad \leq \frac{(q_{k} + \epsilon ) \Delta \epsilon }{\Gamma (\alpha _{k})} \int ^{1}_{0} (1-s)^{\alpha _{k} - 1} \Phi _{k}(s) \,ds \\& \qquad {} + \frac{(1 - \eta _{k} + t ) (q_{k} + \epsilon ) \Delta \epsilon }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{1}_{0} (1 -s)^{\alpha _{k} - 1} \Phi _{k}(s) \,ds \\& \qquad {} + \frac{(1 - \eta _{k} + t ) (q_{k} + \epsilon ) \Delta \epsilon }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{1}_{0} (1 -s)^{\alpha - 1}\Phi _{k}(s) \,ds \\& \qquad {} + \frac{(1 - \eta _{k} + t ) (q_{k} + \epsilon ) \Delta \epsilon }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{1}_{0} (1 -s)^{\alpha _{k} - \mu _{i,k} -1} \Phi _{k}(s) \,ds \\& \quad \leq \frac{(q_{k} + \epsilon ) \Delta \epsilon }{\Gamma (\alpha _{k})} \Vert \hat{\Phi }_{k} \Vert _{[0,1]} + \frac{(1 - \eta _{k} + t ) (q_{k} + \epsilon ) \Delta \epsilon }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \Vert \hat{\Phi }_{k} \Vert _{[0,1]} \\& \qquad {} + \frac{(1 - \eta _{k} + t ) (q_{k} + \epsilon ) \Delta \epsilon }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \Vert \hat{\Phi }_{k} \Vert _{[0,1]} \\& \qquad {} + \frac{(1 - \eta _{k} + t ) (q_{k} + \epsilon ) \Delta \epsilon }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Vert \hat{\Phi }_{k} \Vert _{[0,1]} \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})}. \end{aligned}

Hence,

\begin{aligned}& \bigl\Vert \phi _{k}(x_{1},\ldots, x_{n}) - \phi _{k}(y_{1},\ldots, y_{n}) \bigr\Vert \\& \quad \leq \Biggl( \frac{1}{\Gamma (\alpha _{k})} + \frac{2 (2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \qquad {} + \frac{(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) (q_{k} + \epsilon ) \Delta \Vert \hat{ \Phi }_{k} \Vert _{[0,1]} \epsilon . \end{aligned}

If $$\|(x_{1},\ldots,x_{m}) - (y_{1},\ldots,y_{m})\|_{**} < \epsilon$$ for all $$t \in [0,1]$$ and $$k=1, \ldots, m$$, then we get

\begin{aligned}& \bigl\vert \phi '_{k}(x_{1},\ldots, x_{n}) (t)-\phi '_{k}(y_{1},\ldots, y_{n}) (t) \bigr\vert \\& \quad \leq \frac{1}{\Gamma (\alpha _{k} -1)} \int ^{t}_{0} (t-s)^{ \alpha _{k} - 2} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{1}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) - f_{k} \bigl(s, y_{1}(s), y'_{1}(s), \\& \qquad D^{\beta _{1}}y_{1}(s), I^{p_{1}}y_{1}(s), \ldots, y_{m}(s), y'_{m}(s), D^{\beta _{1}}y_{m}(s), I^{p_{m}}y_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {} + \frac{1}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{1}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) - f_{k} \bigl(s, y_{1}(s), y'_{1}(s), \\& \qquad D^{\beta _{1}}y_{1}(s), I^{p_{1}}y_{1}(s), \ldots, y_{m}(s), y'_{m}(s), D^{\beta _{1}}y_{m}(s), I^{p_{m}}y_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {}+ \frac{1}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{1}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) - f_{k} \bigl(s, y_{1}(s), y'_{1}(s), \\& \qquad D^{\beta _{1}}y_{1}(s), I^{p_{1}}y_{1}(s), \ldots, y_{m}(s), y'_{m}(s), D^{\beta _{1}}y_{m}(s), I^{p_{m}}y_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {} +\frac{1 }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \\& \qquad {}\times\int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{1}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) - f_{k} \bigl(s, y_{1}(s), y'_{1}(s), \\& \qquad D^{\beta _{1}}y_{1}(s), I^{p_{1}}y_{1}(s), \ldots, y_{m}(s), y'_{m}(s), D^{\beta _{1}}y_{m}(s), I^{p_{m}}y_{m}(s) \bigr) \bigr\vert \,ds \\& \quad \leq \frac{1}{\Gamma (\alpha _{k} -1)} \int ^{t}_{0} (t-s)^{ \alpha _{k} - 2} \Phi _{k}(s) M_{k} \bigl( \bigl\vert x_{1}(s) - y_{1}(s) \bigr\vert , \bigl\vert x'_{1}(s) - y_{1}(s) \bigr\vert , \\& \qquad \bigl\vert D^{\beta _{1}}(x_{1}- y_{1}) (s) \bigr\vert , I^{p_{1}}(x_{1} - y_{1}) (s) \vert , \ldots, \bigl\vert x_{m}(s) - y_{m}(s) \bigr\vert , \\& \qquad \bigl\vert x'_{m}(s) - y_{m}(s) \bigr\vert , \bigl\vert D^{\beta _{m}}(x_{m}- y_{m}) (s) \bigr\vert , I^{p_{m}}(x_{m} - y_{m}) (s) \vert \bigr) \,ds \\& \qquad {} + \frac{1 }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \Phi _{k}(s) M_{k} \bigl( \bigl\vert x_{1}(s) - y_{1}(s) \bigr\vert , \bigl\vert x'_{1}(s) - y_{1}(s) \bigr\vert , \\& \qquad {} \bigl\vert D^{\beta _{1}}(x_{1}- y_{1}) (s) \bigr\vert , I^{p_{1}}(x_{1} - y_{1}) (s) \vert , \ldots, \bigl\vert x_{m}(s) - y_{m}(s) \bigr\vert , \\& \qquad \bigl\vert x'_{m}(s) - y_{m}(s) \bigr\vert , \bigl\vert D^{\beta _{m}}(x_{m}- y_{m}) (s) \bigr\vert , I^{p_{m}}(x_{m} - y_{m}) (s) \vert \bigr) \,ds \\& \qquad {}+ \frac{1 }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1}\Phi _{k}(s) M_{k} \bigl( \bigl\vert x_{1}(s) - y_{1}(s) \bigr\vert , \bigl\vert x'_{1}(s) - y_{1}(s) \bigr\vert , \\& \qquad \bigl\vert D^{\beta _{1}}(x_{1}- y_{1}) (s) \bigr\vert , I^{p_{1}}(x_{1} - y_{1}) (s) \vert , \ldots, \bigl\vert x_{m}(s) - y_{m}(s) \bigr\vert , \\& \qquad \bigl\vert x'_{m}(s) - y_{m}(s) \bigr\vert , \bigl\vert D^{\beta _{m}}(x_{m}- y_{m}) (s) \bigr\vert , I^{p_{m}}(x_{m} - y_{m}) (s) \vert \bigr) \,ds \\& \qquad {}+\frac{1}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {}\times \Phi _{k}(s) M_{k} \bigl( \bigl\vert x_{1}(s) - y_{1}(s) \bigr\vert , \bigl\vert x'_{1}(s) - y_{1}(s) \bigr\vert , \bigl\vert D^{\beta _{1}}(x_{1}- y_{1}) (s) \bigr\vert , I^{p_{1}}(x_{1} - y_{1}) (s) \vert \\& \qquad ,\ldots, \bigl\vert x_{m}(s) - y_{m}(s) \bigr\vert , \bigl\vert x'_{m}(s) - y_{m}(s) \bigr\vert , \bigl\vert D^{\beta _{m}}(x_{m}- y_{m}) (s) \bigr\vert , I^{p_{m}}(x_{m} - y_{m}) (s) \vert \bigr) \,ds \\& \quad \leq \frac{ M_{k} ( \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**},\ldots, \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**})}{\Gamma (\alpha _{k} -1)} \\& \qquad {}\times \int ^{1}_{0} (1-s)^{\alpha _{k} - 2} \Phi _{k}(s) \,ds \\& \qquad {}+ \frac{ M_{k} ( \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**},\ldots, \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**})}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \qquad {}\times \int ^{1}_{0} (1 -s)^{\alpha _{k} - 1} \Phi _{k}(s) \,ds \\& \qquad {} + \frac{ M_{k} ( \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**},\ldots, \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**})}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \qquad {} \times \int ^{1}_{0} (1 -s)^{\alpha - 1}\Phi _{k}(s) \,ds \\& \qquad {} + \frac{ M_{k} ( \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**},\ldots, \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**})}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \\& \qquad {}\times \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{1}_{0} (1 -s)^{\alpha _{k} - \mu _{i,k} -1} \Phi _{k}(s) \,ds \\& \quad \leq \frac{(q_{k} + \epsilon ) \Delta \epsilon }{\Gamma (\alpha _{k} -1)} \Vert \hat{\Phi }_{k} \Vert _{[0,1]} + \frac{ (q_{k} + \epsilon ) \Delta \epsilon }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \Vert \hat{\Phi }_{k} \Vert _{[0,1]} \\& \qquad {} + \frac{ (q_{k} + \epsilon ) \Delta \epsilon }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \Vert \hat{\Phi }_{k} \Vert _{[0,1]} \\& \qquad {} + \frac{(q_{k} + \epsilon ) \Delta \epsilon }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Vert \hat{\Phi }_{k} \Vert _{[0,1]} \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})}. \end{aligned}

This implies that

\begin{aligned}& \bigl\Vert \phi '_{k}(x_{1},\ldots, x_{n}) -\phi '_{k}(y_{1},\ldots, y_{n}) \bigr\Vert \\& \quad \leq \Biggl( \frac{1}{\Gamma (\alpha _{k} -1)} + \frac{2}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \qquad {} + \frac{1}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) (q_{k} + \epsilon ) \Delta \Vert \hat{ \Phi }_{k} \Vert _{[0,1]} \epsilon \end{aligned}

and so

\begin{aligned}& \bigl\Vert \phi _{k}(x_{1},\ldots, x_{n}) - \phi _{k}(y_{1},\ldots, y_{n}) \bigr\Vert _{*} \\& \quad = \max \bigl\{ \bigl\Vert \phi _{k}(x_{1},\ldots, x_{n}) -\phi _{k}(y_{1},\ldots, y_{n}) \bigr\Vert , \bigl\Vert \phi '_{k}(x_{1}, \ldots, x_{n}) -\phi '_{k}(y_{1}, \ldots, y_{n}) \bigr\Vert \bigr\} \\& \quad \leq \Biggl( \frac{1}{\Gamma (\alpha _{k} -1)} + \frac{2 (2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \qquad {} + \frac{(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) (q_{k} + \epsilon ) \Delta \Vert \hat{ \Phi }_{k} \Vert _{[0,1]} \epsilon . \end{aligned}

Thus, we get

\begin{aligned}& \bigl\Vert F(x_{1},\ldots, x_{n}) - F(y_{1}, \ldots, y_{n}) \bigr\Vert _{**} \\& \quad = \max_{1 \leq k \leq m} \bigl\Vert \phi _{k}(x_{1}, \ldots, x_{n}) -\phi _{k}(y_{1},\ldots, y_{n}) \bigr\Vert _{*} \\& \quad \leq \max_{1 \leq k \leq m} \Biggl\{ \Biggl( \frac{1}{\Gamma (\alpha _{k} -1)} + \frac{2 (2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \qquad {} + \frac{(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) (q_{k} + \epsilon ) \Delta \Vert \hat{ \Phi }_{k} \Vert _{[0,1]} \Biggr\} \epsilon . \end{aligned}

This implies $$F(x_{1},\ldots, x_{n}) \to F(y_{1},\ldots, y_{n})$$ in $$X^{m}$$ when $$(x_{1},\ldots, x_{n}) \to (y_{1},\ldots, y_{n})$$. Hence, F is continuous on $$X^{m}$$. Since $$\lim_{z \to 0^{+}} \frac{T_{k,j}(t,\Delta z)}{\Delta z} =b_{k,j}(t)$$ for $$1 \leq k \leq m$$ and $$1 \leq j \leq 4m$$, for every $$\epsilon >0$$ we can choose $$\delta (\epsilon )$$ such that $$z \in (0, \delta (\epsilon )]$$ implies $$\frac{T_{k,j}(t,\Delta z)}{\Delta z} \leq b_{k,j}(t) + \epsilon$$ for almost all $$t \in [0,1]$$. Thus,

\begin{aligned} T_{k,j}(t,\Delta z) \leq \bigl(b_{k,j}(t) + \epsilon \bigr) \Delta z \end{aligned}
(6)

for $$z \in (0, \delta (\epsilon )]$$ and almost all $$t \in [0,1]$$. On the other hand, by using the assumptions we have

\begin{aligned}& \max_{1 \leq k \leq m} \Biggl[ \frac{1 }{\Gamma (\alpha _{k} -1)} + \frac{2(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \quad {}+ \frac{(2 - \eta _{k} ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert \Delta < 1. \end{aligned}

Choose $$\epsilon _{0} >0$$ such that

\begin{aligned}& \max_{1 \leq k \leq m} \Biggl( \Biggl[ \frac{1 }{\Gamma (\alpha _{k} -1)} + \frac{2(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \quad {}+ \frac{(2 - \eta _{k} ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert \\& \quad {}+ m \epsilon _{0} \Biggl[ \frac{1 }{\Gamma ^{2} (\alpha _{k} -1)} + \frac{2(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma ^{2} (\alpha _{k})} \\& \quad {}+ \frac{(2 - \eta _{k} ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma ^{2} (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \Biggr) \Delta < 1. \end{aligned}

Since

\begin{aligned}& \max_{1 \leq k \leq m} \Biggl\{ \Biggl( \frac{1}{\Gamma (\alpha _{k} -1)} + \frac{2 (2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \quad {} + \frac{(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) q_{k} \Vert \hat{\Phi }_{k} \Vert _{[0,1]} \Biggr\} \in \biggl[0, \frac{1}{\Delta }\biggr), \end{aligned}

so we can choose $$\epsilon _{1}>0$$ such that

\begin{aligned}& \max_{1 \leq k \leq m} \Biggl\{ \Biggl( \frac{1}{\Gamma (\alpha _{k} -1)} + \frac{2 (2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \quad {} + \frac{(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) (q_{k}+ \epsilon _{1}) \Vert \hat{\Phi }_{k} \Vert _{[0,1]} \Biggr\} \in \biggl[0, \frac{1}{\Delta }\biggr). \end{aligned}

Let $$\delta _{0}= \delta (\epsilon _{0})$$ and put $$r := \min \{ \delta _{0}, \epsilon _{0}, \frac{\delta _{M}(\epsilon _{1})}{2} \}$$. By using (6), $$z \in (0, r]$$ implies

\begin{aligned} T_{k,j}(t,\Delta z) \leq \bigl(b_{k,j}(t) + \epsilon _{0} \bigr) \Delta r \end{aligned}

and specially for $$z=r$$ we have

\begin{aligned} T_{k,j}(t,\Delta r) \leq \bigl(b_{k,j}(t) + \epsilon _{0} \bigr) \Delta r \end{aligned}
(7)

for almost all $$t\in [0,1]$$. Let $$C= \{ (x_{1},\ldots,x_{m}) \in X^{m} : \|(x_{1},\ldots,x_{m})\|_{**} \leq r \}$$. Define the mapping $$\alpha : X^{2m} \to \mathbb{R}$$ by $$\alpha ( (x_{1},\ldots,x_{m}), (y_{1},\ldots,y_{m}) ) =1$$ when $$(x_{1},\ldots,x_{m})$$ and $$(y_{1},\ldots,y_{m})$$ both are in C and $$\alpha ( (x_{1},\ldots,x_{m}), (y_{1},\ldots,y_{m}) ) =0$$ otherwise. If

$$\alpha \bigl( (x_{1},\ldots,x_{m}), (y_{1}, \ldots,y_{m}) \bigr) \geq 1,$$

then $$\|(x_{1},\ldots,x_{m})\|_{**} \leq r$$ and $$\|y_{1},\ldots,y_{m})\|_{**} \leq r$$ and so $$\|x_{k}\|_{*} \leq r$$ and $$\|y_{k}\|_{*} \leq r$$ for all $$1\leq k \leq m$$. Thus, for each $$t \in [0,1]$$, we have

\begin{aligned}& \bigl\vert \phi _{k}(x_{1},\ldots, x_{n}) (t) \bigr\vert \\& \quad \leq \frac{1}{\Gamma (\alpha _{k})} \int ^{t}_{0} (t-s)^{\alpha _{k} - 1} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {} + \frac{1 - \eta _{k} + t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad {}I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {} + \frac{1 - \eta _{k} +t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {}\times \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \bigr\vert \,ds \\& \quad \leq \frac{1}{\Gamma (\alpha _{k})} \int ^{t}_{0} (t-s)^{\alpha _{k} - 1} \bigl[ T_{k,1} \bigl(s, \bigl\vert x_{1}(s) \bigr\vert \bigr)+ T_{k,2} \bigl(s, \bigl\vert x'_{1}(s) \bigr\vert \bigr)+ T_{k,3} \bigl(s, \bigl\vert D^{\beta _{1}}x_{1}(s) \bigr\vert \bigr) \\& \qquad {}+ T_{k,4} \bigl(s, \bigl\vert I^{p_{1}}x_{1}(s) \bigr\vert \bigr) +\cdots+T_{k,4m-3} \bigl(s, \bigl\vert x_{m}(s) \bigr\vert \bigr)+ T_{k,4m-2} \bigl(s, \bigl\vert x'_{m}(s) \bigr\vert \bigr) \\& \qquad {} +T_{k,4m-1} \bigl(s, \bigl\vert D^{\beta _{m}}x_{m}(s) \bigr\vert \bigr) +T_{k,4m} \bigl(s, \bigl\vert I^{p_{m}}x_{m}(s) \bigr\vert \bigr) \bigr] \,ds \\& \qquad {} + \frac{1 - \eta _{k} + t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \bigl[ T_{k,1} \bigl(s, \bigl\vert x_{1}(s) \bigr\vert \bigr)+ T_{k,2} \bigl(s, \bigl\vert x'_{1}(s) \bigr\vert \bigr) \\& \qquad {}+ T_{k,3} \bigl(s, \bigl\vert D^{\beta _{1}}x_{1}(s) \bigr\vert \bigr) + T_{k,4} \bigl(s, \bigl\vert I^{p_{1}}x_{1}(s) \bigr\vert \bigr) +\cdots+T_{k,4m-3} \bigl(s, \bigl\vert x_{m}(s) \bigr\vert \bigr) \\& \qquad {}+ T_{k,4m-2} \bigl(s, \bigl\vert x'_{m}(s) \bigr\vert \bigr) +T_{k,4m-1} \bigl(s, \bigl\vert D^{\beta _{m}}x_{m}(s) \bigr\vert \bigr) +T_{k,4m} \bigl(s, \bigl\vert I^{p_{m}}x_{m}(s) \bigr\vert \bigr) \bigr] \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} \bigl[ T_{k,1} \bigl(s, \bigl\vert x_{1}(s) \bigr\vert \bigr)+ T_{k,2} \bigl(s, \bigl\vert x'_{1}(s) \bigr\vert \bigr) \\& \qquad {}+ T_{k,3} \bigl(s, \bigl\vert D^{\beta _{1}}x_{1}(s) \bigr\vert \bigr) +T_{k,4} \bigl(s, \bigl\vert I^{p_{1}}x_{1}(s) \bigr\vert \bigr) +\cdots+T_{k,4m-3} \bigl(s, \bigl\vert x_{m}(s) \bigr\vert \bigr) \\& \qquad {} + T_{k,4m-2} \bigl(s, \bigl\vert x'_{m}(s) \bigr\vert \bigr)+T_{k,4m-1} \bigl(s, \bigl\vert D^{\beta _{m}}x_{m}(s) \bigr\vert \bigr) +T_{k,4m} \bigl(s, \bigl\vert I^{p_{m}}x_{m}(s) \bigr\vert \bigr) \bigr] \,ds \\& \qquad {} + \frac{1 - \eta _{k} +t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {} \times \bigl[ T_{k,1} \bigl(s, \bigl\vert x_{1}(s) \bigr\vert \bigr)+ T_{k,2} \bigl(s, \bigl\vert x'_{1}(s) \bigr\vert \bigr)+ T_{k,3} \bigl(s, \bigl\vert D^{ \beta _{1}}x_{1}(s) \bigr\vert \bigr) \\& \qquad {} +T_{k,4} \bigl(s, \bigl\vert I^{p_{1}}x_{1}(s) \bigr\vert \bigr) +\cdots+T_{k,4m-3} \bigl(s, \bigl\vert x_{m}(s) \bigr\vert \bigr)+ T_{k,4m-2} \bigl(s, \bigl\vert x'_{m}(s) \bigr\vert \bigr) \\& \qquad {} +T_{k,4m-1} \bigl(s, \bigl\vert D^{\beta _{m}}x_{m}(s) \bigr\vert \bigr) +T_{k,4m} \bigl(s, \bigl\vert I^{p_{m}}x_{m}(s) \bigr\vert \bigr) \bigr] \,ds \\& \quad \leq \frac{1}{\Gamma (\alpha _{k})} \int ^{t}_{0} (t-s)^{\alpha _{k} - 1} \biggl[ T_{k,1} \bigl(s, \Vert x_{1} \Vert \bigr)+ T_{k,2} \bigl(s, \bigl\Vert x'_{1} \bigr\Vert \bigr)+ T_{k,3} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (2- \beta _{1})} \biggr) \\& \qquad {}+ T_{k,4} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (p_{1}+1)} \biggr) + \cdots+T_{k,4m-3} \bigl(s, \Vert x_{m} \Vert \bigr)+ T_{k,4m-2} \bigl(s, \bigl\Vert x'_{m} \bigr\Vert \bigr) \\& \qquad {} +T_{k,4m-1} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (2- \beta _{m})} \biggr) +T_{k,4m} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (p_{m}+1)} \biggr) \biggr] \,ds \\& \qquad {} + \frac{1 - \eta _{k} + t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \biggl[ T_{k,1} \bigl(s, \Vert x_{1} \Vert \bigr)+ T_{k,2} \bigl(s, \bigl\Vert x'_{1} \bigr\Vert \bigr) \\& \qquad {}+ T_{k,3} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (2- \beta _{1})} \biggr) + T_{k,4} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (p_{1}+1)} \biggr) +\cdots+T_{k,4m-3} \bigl(s, \Vert x_{m} \Vert \bigr) \\& \qquad {}+T_{k,4m-2} \bigl(s, \bigl\Vert x'_{m} \bigr\Vert \bigr) +T_{k,4m-1} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (2- \beta _{m})} \biggr) +T_{k,4m} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (p_{m}+1)} \biggr) \biggr] \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} \biggl[ T_{k,1} \bigl(s, \Vert x_{1} \Vert \bigr)+ T_{k,2} \bigl(s, \bigl\Vert x'_{1} \bigr\Vert \bigr) \\& \qquad {}+ T_{k,3} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (2- \beta _{1})} \biggr) + T_{k,4} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (p_{1}+1)} \biggr) +\cdots+T_{k,4m-3} \bigl(s, \Vert x_{m} \Vert \bigr) \\& \qquad {}+T_{k,4m-2} \bigl(s, \bigl\Vert x'_{m} \bigr\Vert \bigr) +T_{k,4m-1} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (2- \beta _{m})} \biggr) +T_{k,4m} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (p_{m}+1)} \biggr) \biggr] \,ds \\& \qquad {}+ \frac{1 - \eta _{k} +t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {} \times \biggl[ T_{k,1} \bigl(s, \Vert x_{1} \Vert \bigr)+ T_{k,2} \bigl(s, \bigl\Vert x'_{1} \bigr\Vert \bigr)+ T_{k,3} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (2- \beta _{1})} \biggr) \\& \qquad {}+T_{k,4} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (p_{1}+1)} \biggr) +\cdots +T_{k,4m-3} \bigl(s, \Vert x_{m} \Vert \bigr) + T_{k,4m-2} \bigl(s, \bigl\Vert x'_{m} \bigr\Vert \bigr) \\& \qquad {}+T_{k,4m-1} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (2- \beta _{m})} \biggr) +T_{k,4m} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (p_{m}+1)} \biggr) \biggr] \,ds \\& \quad \leq \frac{1}{\Gamma (\alpha _{k})} \int ^{t}_{0} (t-s)^{\alpha _{k} - 1} \bigl[ T_{k,1} \bigl(s, \Delta \Vert x_{1} \Vert _{*} \bigr)+ \cdots + T_{k,4} \bigl(s, \Delta \Vert x_{1} \Vert _{*} \bigr) \\& \qquad {}+\cdots +T_{k,4m-3} \bigl(s, \Vert x_{m} \Vert _{*} \bigr)+\cdots+T_{k,4m} \bigl(s, \Vert x_{m} \Vert _{*} \bigr) \bigr] \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \bigl[ T_{k,1} \bigl(s, \Delta \Vert x_{1} \Vert _{*} \bigr) \\& \qquad {}+ \cdots + T_{k,4} \bigl(s, \Delta \Vert x_{1} \Vert _{*} \bigr)+\cdots +T_{k,4m-3} \bigl(s, \Vert x_{m} \Vert _{*} \bigr)+\cdots +T_{k,4m} \bigl(s, \Vert x_{m} \Vert _{*} \bigr) \bigr] \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} \bigl[ T_{k,1} \bigl(s, \Delta \Vert x_{1} \Vert _{*} \bigr) \\& \qquad {}+ \cdots + T_{k,4} \bigl(s, \Delta \Vert x_{1} \Vert _{*} \bigr)+\cdots +T_{k,4m-3} \bigl(s, \Vert x_{m} \Vert _{*} \bigr)+\cdots +T_{k,4m} \bigl(s, \Vert x_{m} \Vert _{*} \bigr) \bigr] \,ds \\& \qquad {}+ \frac{1 - \eta _{k} +t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {} \times \bigl[ T_{k,1} \bigl(s, \Delta \Vert x_{1} \Vert _{*} \bigr)+ \cdots + T_{k,4} \bigl(s, \Delta \Vert x_{1} \Vert _{*} \bigr) \\& \qquad {}+\cdots +T_{k,4m-3} \bigl(s, \Vert x_{m} \Vert _{*} \bigr)+\cdots+T_{k,4m} \bigl(s, \Vert x_{m} \Vert _{*} \bigr) \bigr] \,ds \\& \quad \leq \frac{1}{\Gamma (\alpha _{k})} \int ^{t}_{0} (t-s)^{\alpha _{k} - 1} \bigl[ T_{k,1}(s, \Delta r)+ \cdots+T_{k,4m}(s, \Delta r) \bigr] \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \bigl[ T_{k,1}(s, \Delta r)+ \cdots+T_{k,4m}(s, \Delta r) \bigr] \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} \bigl[ T_{k,1}(s, \Delta r)+ \cdots+T_{k,4m}(s, \Delta r) \bigr] \,ds \\& \qquad {}+ \frac{1 - \eta _{k} +t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {} \times \bigl[ T_{k,1}(s, \Delta r)+ \cdots+T_{k,4m}(s, \Delta r) \bigr] \,ds. \end{aligned}

Now by using (5), we obtain

\begin{aligned}& \bigl\vert \phi _{k}(x_{1},\ldots, x_{n}) (t) \bigr\vert \\& \quad \leq \frac{1}{\Gamma (\alpha _{k})} \int ^{1}_{0} (1-s)^{\alpha _{k} - 1} \Biggl[ \sum _{j=1}^{m} \bigl(b_{k,j}(s)+ \epsilon _{0} \bigr) \Delta r \Biggr] \,ds \\& \qquad {}+ \frac{1 - \eta _{k} + t }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{1}_{0} (1 -s)^{\alpha - 1} \Biggl[ \sum _{j=1}^{m} \bigl(b_{k,j}(s)+ \epsilon _{0} \bigr) \Delta r \Biggr] \,ds \\& \qquad {}+ \frac{1 - \eta _{k} +t}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{1}_{0} (1 -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {}\times \Biggl[ \sum_{j=1}^{m} \bigl(b_{k,j}(s)+\epsilon _{0} \bigr) \Delta r \Biggr] \,ds \\& \quad \leq \frac{\Delta r }{\Gamma (\alpha _{k})} \sum_{j=1}^{m} \biggl[ \int ^{1}_{0} (1-s)^{\alpha _{k} - 2} b_{k,j}(s) \,ds+ \epsilon _{0} \int ^{1}_{0} (1-s)^{\alpha _{k} - 1} \,ds \biggr] \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \sum_{j=1}^{m} \biggl[ \int ^{1}_{0} (1-s)^{\alpha _{k} - 2} b_{k,j}(s) \,ds+ \epsilon _{0} \int ^{1}_{0} (1-s)^{\alpha _{k} - 1} \,ds \biggr] \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \sum_{j=1}^{m} \biggl[ \int ^{1}_{0} (1-s)^{\alpha _{k} - 2} b_{k,j}(s) \,ds+ \epsilon _{0} \int ^{1}_{0} (1-s)^{\alpha _{k} - 1} \,ds \biggr] \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \\& \qquad {}\times \Biggl( \sum_{j=1}^{m} \biggl[ \int ^{1}_{0} (1-s)^{\alpha _{k} - 2} b_{k,j}(s) \,ds+ \epsilon _{0} \int ^{1}_{0} (1-s)^{\alpha _{k} - \mu _{i,k} -1} \,ds \biggr] \Biggr) \\& \quad \leq \frac{\Delta r }{\Gamma (\alpha _{k})} \sum_{j=1}^{m} \biggl( \Vert \hat{b}_{k,j} \Vert + \frac{\epsilon _{0}}{\Gamma (\alpha _{k})} \biggr) \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \sum_{j=1}^{m} \biggl( \Vert \hat{b}_{k,j} \Vert + \frac{\epsilon _{0}}{\Gamma (\alpha _{k})} \biggr) \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \sum_{j=1}^{m} \biggl( \Vert \hat{b}_{k,j} \Vert + \frac{\epsilon _{0}}{\Gamma (\alpha _{k})} \biggr) \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \Biggl[ \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \sum_{j=1}^{m} \biggl( \Vert \hat{b}_{k,j} \Vert + \frac{\epsilon _{0}}{\Gamma (\alpha _{k} - \mu _{i,k})} \biggr) \Biggr] \\& \quad = \frac{\Delta r }{\Gamma (\alpha _{k})} \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert + \frac{m \epsilon _{0}}{\Gamma ^{2}(\alpha _{k})} \Delta r \\& \qquad {}+ \frac{2(1 - \eta _{k} + t ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert + \frac{2 (1 - \eta _{k} + t ) m \epsilon _{0}}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma ^{2}(\alpha _{k})} \Delta r \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggl( \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert \Biggr) \\& \qquad {}+ \frac{ (1 - \eta _{k} + t ) m \epsilon _{0}}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma ^{2} (\alpha _{k} -\mu _{i,k})} \Delta r \\& \quad = \Biggl( \Biggl[ \frac{1 }{\Gamma (\alpha _{k})} + \frac{2(1 - \eta _{k} + t ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert \\& \qquad {}+ m \epsilon _{0} \Biggl[ \frac{1 }{\Gamma ^{2} (\alpha _{k})} + \frac{2(1 - \eta _{k} + t ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma ^{2} (\alpha _{k})} \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum _{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma ^{2} (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \Biggr) \Delta r \end{aligned}

and so

\begin{aligned}& \bigl\Vert \phi _{k}(x_{1},\ldots, x_{n}) \bigr\Vert \\& \quad \leq \Biggl( \Biggl[ \frac{1 }{\Gamma (\alpha _{k})} + \frac{2(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})}\\& \qquad {} + \frac{(2 - \eta _{k} ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert \\& \qquad {}+ m \epsilon _{0} \Biggl[ \frac{1 }{\Gamma ^{2} (\alpha _{k})} + \frac{2(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma ^{2} (\alpha _{k})} \\& \qquad {}+ \frac{(2 - \eta _{k} ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum _{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma ^{2} (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \Biggr) \Delta r. \end{aligned}

Hence,

\begin{aligned}& \bigl\Vert \phi _{k}(x_{1},\ldots, x_{n}) \bigr\Vert \\& \quad \leq \Biggl( \Biggl[ \frac{1 }{\Gamma (\alpha _{k} -1)} + \frac{2(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \qquad {}+ \frac{(2 - \eta _{k} ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert \\& \qquad {}+ m \epsilon _{0} \Biggl[ \frac{1 }{\Gamma ^{2} (\alpha _{k} -1)} + \frac{2(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma ^{2} (\alpha _{k})} \\& \qquad {}+ \frac{(2 - \eta _{k} ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum _{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma ^{2} (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \Biggr) \Delta r \\& \quad \leq r. \end{aligned}

Let $$t \in [0,1]$$, $$1 \leq k \leq m$$ and $$(x_{1},\ldots, x_{n}) \in C$$. Then we have

\begin{aligned}& \bigl\vert \phi '_{k}(x_{1},\ldots, x_{n}) (t) \bigr\vert \\& \quad \leq \frac{1}{\Gamma (\alpha _{k} -1)} \int ^{t}_{0} (t-s)^{ \alpha _{k} - 2} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{1}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {} + \frac{1}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{1}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {}+ \frac{1 }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), \\& \qquad I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \bigr\vert \,ds \\& \qquad {} +\frac{1 }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {}\times \bigl\vert f_{k} \bigl(s, x_{1}(s), x'_{1}(s), D^{\beta _{1}}x_{1}(s), I^{p_{1}}x_{1}(s),\ldots, x_{m}(s), x'_{m}(s), D^{\beta _{m}}x_{m}(s), I^{p_{m}}x_{m}(s) \bigr) \bigr\vert \,ds \\& \quad \leq \frac{1}{\Gamma (\alpha _{k} -1)} \int ^{t}_{0} (t-s)^{ \alpha _{k} - 2} \biggl[ T_{k,1} \bigl(s, \Vert x_{1} \Vert \bigr)+ T_{k,2} \bigl(s, \bigl\Vert x'_{1} \bigr\Vert \bigr)+ T_{k,3} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (2- \beta _{1})} \biggr) \\& \qquad {}+ T_{k,4} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (p_{1}+1)} \biggr) + \cdots+T_{k,4m-3} \bigl(s, \Vert x_{m} \Vert \bigr)+ T_{k,4m-2} \bigl(s, \bigl\Vert x'_{m} \bigr\Vert \bigr) \\& \qquad {} +T_{k,4m-1} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (2- \beta _{m})} \biggr) +T_{k,4m} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (p_{m}+1)} \biggr) \biggr] \,ds \\& \qquad {} + \frac{1}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \biggl[ T_{k,1} \bigl(s, \Vert x_{1} \Vert \bigr)+ T_{k,2} \bigl(s, \bigl\Vert x'_{1} \bigr\Vert \bigr) \\& \qquad {}+ T_{k,3} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (2- \beta _{1})} \biggr) + T_{k,4} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (p_{1}+1)} \biggr) +\cdots+T_{k,4m-3} \bigl(s, \Vert x_{m} \Vert \bigr) \\& \qquad {}+T_{k,4m-2} \bigl(s, \bigl\Vert x'_{m} \bigr\Vert \bigr) +T_{k,4m-1} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (2- \beta _{m})} \biggr) +T_{k,4m} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (p_{m}+1)} \biggr) \biggr] \,ds \\& \qquad {}+ \frac{1 }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} \biggl[ T_{k,1} \bigl(s, \Vert x_{1} \Vert \bigr)+ T_{k,2} \bigl(s, \bigl\Vert x'_{1} \bigr\Vert \bigr) \\& \qquad {}+ T_{k,3} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (2- \beta _{1})} \biggr) + T_{k,4} \biggl(s, \frac{ \Vert x_{1} \Vert }{\Gamma (p_{1}+1)} \biggr) +\cdots+T_{k,4m-3} \bigl(s, \Vert x_{m} \Vert \bigr) \\& \qquad {}+T_{k,4m-2} \bigl(s, \bigl\Vert x'_{m} \bigr\Vert \bigr) +T_{k,4m-1} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (2- \beta _{m})} \biggr) +T_{k,4m} \biggl(s, \frac{ \Vert x_{m} \Vert }{\Gamma (p_{m}+1)} \biggr) \biggr] \,ds \\& \quad \leq \frac{1}{\Gamma (\alpha _{k} -1)} \int ^{t}_{0} (t-s)^{ \alpha _{k} - 2} \bigl[ T_{k,1}(s, \Delta r)+ \cdots+T_{k,4m}(s, \Delta r) \bigr] \,ds \\& \qquad {}+ \frac{1 }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\theta _{k}}_{0} (\theta _{k} -s)^{\alpha _{k} - 1} \bigl[ T_{k,1}(s, \Delta r)+ \cdots+T_{k,4m}(s, \Delta r) \bigr] \,ds \\& \qquad {}+ \frac{1 }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{\eta _{k}}_{0} (\eta _{k} -s)^{\alpha - 1} \bigl[ T_{k,1}(s, \Delta r)+ \cdots+T_{k,4m}(s, \Delta r) \bigr] \,ds \\& \qquad {}+\frac{1 }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{ \gamma _{i,k}}_{0} (\gamma _{i,k} -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {}\times \bigl[ T_{k,1}(s, \Delta r)+ \cdots+T_{k,4m}(s, \Delta r) \bigr] \,ds \\& \quad \leq \frac{1}{\Gamma (\alpha _{k} -1)} \int ^{1}_{0} (1-s)^{ \alpha _{k} - 2} \Biggl[ \sum _{j=1}^{m} \bigl(b_{k,j}(s)+ \epsilon _{0} \bigr) \Delta r \Biggr] \,ds \\& \qquad {}+ \frac{2}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \int ^{1}_{0} (1 -s)^{\alpha - 1} \Biggl[ \sum _{j=1}^{m} \bigl(b_{k,j}(s)+ \epsilon _{0} \bigr) \Delta r \Biggr] \,ds \\& \qquad {}+\frac{1 }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \int ^{1}_{0} (1 -s)^{\alpha _{k} - \mu _{i,k} -1} \\& \qquad {}\times \Biggl[ \sum_{j=1}^{m} \bigl(b_{k,j}(s)+\epsilon _{0} \bigr) \Delta r \Biggr] \,ds \\& \quad \leq \frac{\Delta r }{\Gamma (\alpha _{k} -2)} \sum_{j=1}^{m} \biggl[ \int ^{1}_{0} (1-s)^{\alpha _{k} - 2} b_{k,j}(s) \,ds+ \epsilon _{0} \int ^{1}_{0} (1-s)^{\alpha _{k} - 2} \,ds \biggr] \\& \qquad {}+ \frac{2 \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \sum_{j=1}^{m} \biggl[ \int ^{1}_{0} (1-s)^{\alpha _{k} - 2} b_{k,j}(s) \,ds+ \epsilon _{0} \int ^{1}_{0} (1-s)^{\alpha _{k} - 1} \,ds \biggr] \\& \qquad {}+ \frac{ \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \\& \qquad {}\times \Biggl( \sum_{j=1}^{m} \biggl[ \int ^{1}_{0} (1-s)^{\alpha _{k} - 2} b_{k,j}(s) \,ds+ \epsilon _{0} \int ^{1}_{0} (1-s)^{\alpha _{k} - \mu _{i,k} -1} \,ds \biggr] \Biggr) \\& \quad = \frac{\Delta r }{\Gamma (\alpha _{k} -1)} \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert + \frac{m \epsilon _{0}}{\Gamma ^{2}(\alpha _{k} -1)} \Delta r \\& \qquad {}+ \frac{2 \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert + \frac{2 m \epsilon _{0}}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma ^{2}(\alpha _{k})} \Delta r \\& \qquad {}+ \frac{ \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggl( \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert \Biggr) \\& \qquad {}+ \frac{ m \epsilon _{0}}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma ^{2} (\alpha _{k} -\mu _{i,k})} \Delta r. \end{aligned}

Thus, we get

\begin{aligned}& \bigl\Vert \phi '_{k}(x_{1},\ldots, x_{n}) \bigr\Vert \\& \quad \leq \Biggl( \Biggl[ \frac{1 }{\Gamma (\alpha _{k} -1)} + \frac{2(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \qquad {}+ \frac{(2 - \eta _{k} ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \sum_{j=1}^{m} \Vert \hat{b}_{k,j} \Vert \\& \qquad {}+ m \epsilon _{0} \Biggl[ \frac{1 }{\Gamma ^{2} (\alpha _{k} -1)} + \frac{2(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma ^{2} (\alpha _{k})} \\& \qquad {}+ \frac{(2 - \eta _{k} ) \Delta r}{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum _{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma ^{2} (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \Biggr) \Delta r \\& \quad \leq r \end{aligned}

and so $$\|\phi _{k}(x_{1},\ldots, x_{n}) \|_{*} \leq r$$ for all $$1 \leq k \leq m$$. Hence,

$$\bigl\Vert F(x_{1},\ldots, x_{n}) \bigr\Vert _{**} = \max_{1 \leq k \leq m} \bigl\Vert \phi _{k}(x_{1},\ldots, x_{n}) \bigr\Vert _{*} \leq r$$

and so $$F(x_{1},\ldots, x_{n}) \in C$$. For similar reasons, we find $$F(y_{1},\ldots, y_{n}) \in C$$ and so

$$\alpha \bigl(F(x_{1},\ldots, x_{n}), F(y_{1}, \ldots, y_{n}) \bigr) \geq 1.$$

Since $$C \neq \phi$$, for each $$(x_{1},\ldots, x_{n}) \in C$$, $$F(x_{1},\ldots, x_{n}) \in C$$ and so

$$\alpha \bigl((x_{1},\ldots, x_{n}), F(x_{1}, \ldots, x_{n}) \bigr) \geq 1.$$

Let

\begin{aligned} \lambda &:= \max_{1 \leq k \leq m} \Biggl\{ \Biggl( \frac{1}{\Gamma (\alpha _{k} -1)} + \frac{2 (2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\ &\quad {}+ \frac{(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) q_{k} \Vert \hat{\Phi }_{k} \Vert _{[0,1]} \Biggr\} \Delta \\ &< 1 \end{aligned}

and $$(x_{1},\ldots, x_{n}), (y_{1},\ldots, y_{n}) \in C$$, Then $$\alpha ((x_{1},\ldots, x_{n}), (y_{1},\ldots, y_{n}) ) = 1$$. On the other hand by using (4), for each $$(x_{1},\ldots, x_{n}), (y_{1},\ldots, y_{n}) \in X^{m}$$, $$t \in [0,1]$$ and $$1 \leq k \leq m$$ we have

\begin{aligned}& \bigl\vert \phi _{k}(x_{1},\ldots, x_{n}) (t)-\phi _{k}(y_{1},\ldots, y_{n}) (t) \bigr\vert \\& \quad \leq \frac{ M_{k} ( \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**},\ldots, \Delta \Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \Vert _{**})}{\Gamma (\alpha _{k})} \Vert \hat{\Phi _{k}} \Vert \\& \qquad {}+ \bigl((1 - \eta _{k} + t ) M_{k} \bigl( \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**},\ldots,\\& \qquad \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**}\bigr)/\bigl( \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})\bigr)\bigr) \Vert \hat{\Phi _{k}} \Vert \\& \qquad {}+ \bigl((1 - \eta _{k} + t ) M_{k} \bigl( \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**},\ldots,\\& \qquad \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**}\bigr)/\bigl( \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})\bigr)\bigr) \Vert \hat{\Phi _{k}} \Vert \\& \qquad {}+ (1 - \eta _{k} + t ) M_{k} \bigl( \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**},\ldots,\\& \qquad \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**}\bigr)/\bigl( \bigl\vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \bigr\vert \bigr) \\& \qquad {}\times \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Vert \hat{\Phi _{k}} \Vert . \end{aligned}

Since $$(x_{1},\ldots, x_{n}), (y_{1},\ldots, y_{n}) \in C$$, $$\| (x_{1},\ldots, x_{n}) \|_{**} \leq r$$ and $$\| (y_{1},\ldots, y_{n}) \|_{**} \leq r$$. Thus,

\begin{aligned}& \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1}, \ldots, y_{n}) \bigr\Vert _{**} \\& \quad \leq \bigl\Vert (x_{1},\ldots, x_{n}) \bigr\Vert _{**} + \bigl\Vert (y_{1},\ldots, y_{n}) \bigr\Vert _{**} \leq r + r \leq \frac{\delta _{M}}{2} + \frac{\delta _{M}}{2} = \delta _{M}. \end{aligned}

By using (5), for each $$1 \leq k \leq m$$ we get

\begin{aligned}& M_{k} \bigl(\Delta \bigl\Vert (x_{1},\ldots, x_{n}) \bigr\Vert _{**} - \bigl\Vert (y_{1}, \ldots, y_{n}) \bigr\Vert _{**} ,\ldots, \Delta \bigl\Vert (x_{1},\ldots, x_{n}) \bigr\Vert _{**} - \bigl\Vert (y_{1},\ldots, y_{n}) \bigr\Vert _{**} \bigr) \\& \quad < (q_{k} + \epsilon _{1}) \Delta \bigl\Vert (x_{1},\ldots, x_{n}) \bigr\Vert _{**} - \bigl\Vert (y_{1},\ldots, y_{n}) \bigr\Vert _{**} \end{aligned}

and so

\begin{aligned}& \bigl\vert \phi _{k}(x_{1},\ldots, x_{n}) (t)-\phi _{k}(y_{1},\ldots, y_{n}) (t) \bigr\vert \\& \quad \leq \frac{\hat{\| \Phi _{k}} \| }{\Gamma (\alpha _{k})} (q_{k} + \epsilon _{1}) \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**} \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \Vert \hat{\Phi _{k}} \Vert (q_{k} + \epsilon _{1}) \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**} \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \Vert \hat{\Phi _{k}} \Vert (q_{k} + \epsilon _{1}) \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**} \\& \qquad {}+ \frac{(1 - \eta _{k} + t ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \\& \qquad {}\times \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Vert \hat{\Phi _{k}} \Vert (q_{k} + \epsilon _{1}) \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**}. \end{aligned}

It implies that

\begin{aligned}& \bigl\Vert \phi _{k}(x_{1},\ldots, x_{n}) - \phi _{k}(y_{1},\ldots, y_{n}) \bigr\Vert \\& \quad \leq \Biggl( \frac{1 }{\Gamma (\alpha _{k})} + \frac{2 (2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} + \frac{(1 - \eta _{k} + t ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr) \\& \qquad {}\times (q_{k} + \epsilon _{1}) \Delta \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**} \\& \quad \leq \lambda \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**} \end{aligned}

and so

\begin{aligned}& \bigl\Vert \phi _{k}(x_{1},\ldots, x_{n}) - \phi _{k}(y_{1},\ldots, y_{n}) \bigr\Vert \leq \lambda \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**}. \end{aligned}

Similarly, we can find

$$\bigl\Vert \phi '_{k}(x_{1}, \ldots, x_{n}) -\phi '_{k}(y_{1}, \ldots, y_{n}) \bigr\Vert \leq \lambda \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**}$$

and so $$\|\phi _{k}(x_{1},\ldots, x_{n}) -\phi _{k}(y_{1},\ldots, y_{n}) \| _{*} \leq \lambda \|(x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n})\|_{**}$$. Hence,

\begin{aligned} \bigl\Vert F(x_{1},\ldots, x_{n}) - F(y_{1}, \ldots, y_{n}) \bigr\Vert _{**} =& \max _{1 \leq k \leq m} \bigl\Vert \phi _{k}(x_{1}, \ldots, x_{n}) -\phi _{k}(y_{1},\ldots, y_{n}) \bigr\Vert _{*} \\ \leq& \lambda \bigl\Vert (x_{1},\ldots, x_{n})- (y_{1},\ldots, y_{n}) \bigr\Vert _{**}. \end{aligned}
(8)

Now, consider the map $$\psi : [0, \infty ) \to [0, \infty )$$ defined by $$\psi (t)= \lambda t$$. If $$(x_{1},\ldots, x_{n}) \notin C$$ or $$(y_{1},\ldots, y_{n}) \notin C$$, then $$\alpha ((x_{1},\ldots, x_{n}), (y_{1},\ldots, y_{n}) ) = 0$$ and so

\begin{aligned}& \alpha \bigl((x_{1},\ldots, x_{n}), (y_{1}, \ldots, y_{n}) \bigr) \,d \bigl(F(x_{1},\ldots, x_{n}), F(y_{1},\ldots, y_{n}) \bigr) \\& \quad \leq \psi \bigl((x_{1},\ldots, x_{n}), (y_{1},\ldots, y_{n}) \bigr). \end{aligned}

If $$(x_{1},\ldots, x_{n})$$, $$(y_{1},\ldots, y_{n}) \notin C$$, then $$\alpha ((x_{1},\ldots, x_{n}), (y_{1},\ldots, y_{n}) ) =1$$ and so by using (8), we obtain

\begin{aligned}& \alpha \bigl((x_{1},\ldots, x_{n}), (y_{1}, \ldots, y_{n}) \bigr) \,d \bigl(F(x_{1},\ldots, x_{n}), F(y_{1},\ldots, y_{n}) \bigr) \\& \quad \leq \psi \bigl((x_{1},\ldots, x_{n}), (y_{1},\ldots, y_{n}) \bigr). \end{aligned}

Now by using Lemma 1.1, we conclude that F has a fixed point in $$X^{m}$$ which is a solution for the problem. □

Here, we present an example to illustrate our main result.

### Example 2.3

Consider the pointwise defined problem

\begin{aligned} \textstyle\begin{cases} D^{\frac{5}{2}} x(t) = f_{1}(t, x(t), x'(t), D^{\frac{1}{2}}x(t), I^{ \frac{1}{3}}x(t), y(t), y'(t), D^{\frac{1}{3}}y(t), I^{\frac{1}{2}}y(t)), \\ D^{\frac{7}{3}} y(t) =f_{2}(t, x(t), x'(t), D^{\frac{1}{2}}x(t), I^{ \frac{1}{3}}x(t), y(t), y'(t), D^{\frac{1}{3}}y(t), I^{\frac{1}{2}}y(t)), \end{cases}\displaystyle \end{aligned}
(9)

with boundary conditions $$x^{\prime \prime }(0)= y^{\prime \prime }(0)=0$$, $$x(\frac{1}{2})=y(\frac{1}{2})= D^{\frac{1}{2} }x(\frac{1}{3})$$, $$x'(0)= x(\frac{1}{4})$$ and $$y'(0)= y(\frac{1}{3})$$, where $$f_{1}(t, x_{1},\ldots, x_{8})= \sum_{j=1}^{8} \frac{1}{t^{\sigma _{j}}} |x_{j}|$$, $$f_{2}(t, x_{1},\ldots, x_{8})=\frac{c(t)}{p(t)} \sum_{j=1}^{8} |x_{j}|$$, $$c(t)=1$$ and $$p(t)=0$$ whenever $$t\in [0, 1]\cap \mathbb{Q}$$, $$c(t)=0$$ and $$p(t)=1$$ whenever $$t\in [0, 1]\cap \mathbb{Q}^{c}$$ and $$\sigma _{1},\ldots, \sigma _{8} \in (0,\frac{1}{2})$$. Note that

\begin{aligned}& \bigl\vert f_{1}(t, x_{1},\ldots. x_{8}) - f_{1}(t, y_{1},\ldots,y_{8}) \bigr\vert \leq \sum_{k=1}^{8} \frac{1}{50 t^{\sigma _{i}}} \vert x_{k} - y_{k} \vert , \\& \bigl\vert f_{2}(t, x_{1},\ldots. x_{8}) - f_{2}(t, y_{1},\ldots,y_{8}) \bigr\vert \leq \frac{c(t)}{40 p(t)} \sum_{k=1}^{8} \vert x_{k} - y_{k} \vert , \\& \bigl\vert f_{1}(t, x_{1}, \ldots, x_{8}) - f_{1}(t, y_{1}, \ldots, y_{8}) \bigr\vert \leq \Phi _{1}(t) M_{1} \bigl( \vert x_{1} - y_{1} \vert , \ldots, \vert x_{8} - y_{8} \vert \bigr) \end{aligned}

and $$|f_{2}(t, x_{1}, \ldots, x_{4m}) - f_{1}(t, y_{1}, \ldots, y_{4m})| \leq \Phi _{2}(t) M_{2}(|x_{1} - y_{1}|, \ldots, |x_{8} - y_{8}|)$$, where $$\Phi _{1}(t) = \frac{1}{50t^{\sigma }}$$, $$\Phi _{2}(t) = \frac{c(t)}{40p(t)}$$, $$\sigma := \min \{\sigma _{1}, \ldots, \sigma _{8} \}$$ $$M_{1}(x_{1} , \ldots, x_{8} ) = M_{2}(x_{1}, \ldots, x_{8})=\sum_{k=1}^{8} |x_{k} |$$. Also,

$$\bigl\vert f_{k}(t, x_{1}, \ldots, x_{8}) \bigr\vert \leq \sum_{j=1}^{8} T_{k,j} \bigl(t, \vert x_{k} \vert \bigr)$$

for $$k =1,2$$, where $$T_{1,j}(t, |x_{k}|) = \frac{1}{50 t^{\sigma _{j}}} |x_{j}|$$ and $$T_{2,j}(t, |x_{k}|) = \frac{c(t)}{40 p(t)} |x_{j}|$$ for $$j =1, \dots , 8$$. Then $$M_{k} :X^{8} \to \mathbb{R}^{+}$$ is nondecreasing with respect to all components, $$\lim_{z \to 0^{+}} \frac{M_{k}(z,\ldots,z)}{z}= 8 :=q_{k} \in [0, \infty )$$ for $$k =1,2$$, $$T_{k,j}(\cdot,z)$$ is nondecreasing with respect to z, $$\lim_{z \to 0^{+}} \frac{T_{1,j}(t,z)}{z} = \frac{1}{50 t^{\sigma _{j}}} :=b_{1,j}(s)$$,

$$\lim_{z \to 0^{+}} \frac{T_{2,j}(t,z)}{z} =\frac{c(t)}{40 p(t)} :=b_{1,j}(s)$$

for $$j =1, \ldots, 8$$ and almost all $$t \in [0,1]$$, $$\| \hat{\phi }_{1}\| \leq \frac{1}{50(1- \sigma )}$$, $$\| \hat{\phi }_{2}\| \leq \frac{1}{60}$$ $$\| \hat{b}_{1,j}\| \leq \frac{1}{50(1- \sigma _{j})}$$, $$\| \hat{b}_{2,j}\| \leq \frac{1}{60}$$,

\begin{aligned} \Delta _{\gamma _{1}} =& \Delta _{\gamma _{2}} =\sum _{i=1}^{n_{0}} \frac{\lambda _{i,k} (\gamma _{i,k})^{1- \mu _{i,k}}}{\Gamma (2 -\mu _{i,k})} \\ =& \frac{\lambda _{1} (\gamma _{1})^{1- \mu _{1}}}{\Gamma (2 -\mu _{1})} = \frac{ (\frac{1}{3})^{\frac{1}{2}}{\Gamma (\frac{3}{2})}}{\Gamma (2 -\mu _{1})} \frac{2}{\sqrt{3 \pi }} \end{aligned}

and $$1- \Delta _{\gamma _{k}} \neq \eta _{k} - \theta _{k}$$. Put

\begin{aligned} \Delta =& \max \biggl\{ 1, \frac{1}{\Gamma (2- \beta _{1})}, \frac{1}{\Gamma (2- \beta _{2})}, \frac{1}{\Gamma (p_{1} +1)}, \frac{1}{\Gamma (p_{m} +1)} \biggr\} \\ =& \max \biggl\{ 1, \frac{1}{\Gamma (\frac{3}{2})}, \frac{1}{\Gamma (\frac{5}{3})}, \frac{1}{\Gamma (\frac{5}{3})}, \frac{1}{\Gamma (\frac{1}{2})} \biggr\} =\frac{2}{\sqrt{\pi }}. \end{aligned}

Then we have

\begin{aligned}& \max_{1 \leq k \leq m} \Biggl[ \frac{1 }{\Gamma (\alpha _{k} -1)} + \frac{2(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert \Gamma (\alpha _{k})} \\& \quad {}+ \frac{(2 - \eta _{k} ) }{ \vert \Delta _{\gamma _{k}} - \theta _{k} - 1 +\eta _{k} \vert } \Biggl( \sum_{i=1}^{n_{0}} \frac{\lambda _{i,k}}{\Gamma (\alpha _{k} -\mu _{i,k})} \Biggr) \Biggr] \max \Biggl\{ \sum _{j=1}^{m} \Vert \hat{b}_{k,j} \Vert , q_{k} \hat{\Phi }_{k} \Biggr\} \\& \quad \max \biggl\{ \biggl[ \frac{1 }{\Gamma (\frac{3}{2})} + \frac{2(\frac{7}{4} ) }{ \vert \frac{2}{\sqrt{3 \pi }} - \theta _{k} - 1 + \frac{1}{4} \vert \Gamma (\frac{5}{2})} + \frac{\frac{7}{4}}{ \vert \frac{2}{\sqrt{3 \pi }} - \frac{1}{2} - 1 +\frac{7}{4} \vert } \biggl( \frac{1}{\Gamma (2)} \biggr) \biggr] \times \frac{16}{50}, \\& \quad \biggl[ \frac{1 }{\Gamma (\frac{5}{2})} + \frac{2(\frac{5}{3} ) }{ \vert \frac{2}{\sqrt{3 \pi }} - \frac{1}{2}- 1 + \frac{1}{3} \vert \Gamma (\frac{7}{2})} + \frac{\frac{5}{3}}{ \vert \frac{2}{\sqrt{3 \pi }} - \frac{1}{2} - 1 +\frac{7}{4} \vert } \biggl( \frac{1}{\Gamma (3)} \biggr) \biggr] \times \frac{2}{15}\biggr\} \in \biggl[0, \frac{1}{\Delta }\biggr). \end{aligned}

Now by using Theorem 2.2, problem (9) has a solution.

## 3 Conclusion

Some phenomena could be modeled by singular fractional differential equations. By studying multi-singular fractional differential equations we like to increase our abilities in modeling complicated phenomena in the world. In this work by using α-ψ-contractions and locating some control conditions, we investigate the existence of solutions for a multi-singular fractional differential system. Also, we present an example to illustrate our main result.

## Availability of data and materials

Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.

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### Acknowledgements

The first author was supported by South Tehran Branch, Islamic Azad University. The second author was supported by Azarbaijan Shahid Madani University. The third author was supported by Meharn Branch, Islamic Azad University. The authors express their gratitude dear unknown referees for their helpful suggestions which improved final version of this paper.

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(Ali Mansouri: s_t_mansouri@azad.ac.ir and Mehdi Shabibi: mehdi_math1983@yahoo.com)

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The authors declare that the study was realized in collaboration with equal responsibility. All authors read and approved the final manuscript.

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Correspondence to Shahram Rezapour.

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Mansouri, A., Rezapour, S. & Shabibi, M. On the existence of solutions for a multi-singular pointwise defined fractional system. Adv Differ Equ 2020, 646 (2020). https://doi.org/10.1186/s13662-020-03106-w