1. Introduction
FCs ware first employed in 1695 when L’Hopital summarized his discoveries in a letter to Leibniz. Fractional calculus (FCs) was studied by several twentieth century authors, including Liouville, Grunwald, Letnikov, and Riemann. This field of mathematics, known as fractional differential equations, was invented by mathematicians as a pure branch of mathematics with just a few applications in mathematics. Fractional calculus is a well-established subject with applications in many applied sciences, such as visco-elasticity, medical, and environment, which leads the fractional differential equations to become extremely prevalent. We recommend the monographs [
1,
2,
3,
4,
5,
6,
7,
8] and the recently mentioned papers [
9,
10,
11,
12,
13,
14,
15,
16,
17]. It is worth noting that most of the works in the field of fractional differentiation focus mostly on R-L and Caputo types. See [
18,
19,
20,
21,
22].
In 1772, Russian scientists presented a general idea of stability, such as Lyapunov (1758–1817), where the general theme of his doctoral dissertation was movement stability, and his work soon spread all over Russia and later in the West. With the process of research, scientists entered the time delay, and the first to describe these systems with a time delay was the scientist (Boltzman), who studied its effect but did not refer to the time delay in realistic models.
In the early 1900s, a disagreement arose over the necessity of introducing time delays into systems to predict their future development, but this point of view contradicted the Newtonian traditions, which claimed that knowledge of the current values of all relevant variables should suffice for the prediction. Ulam and Hyers, on the other hand, recognized unknown types of stability known as ulam-stability. Hyer’s type of stability study contributes expressively to our understanding of population dynamics and fluid movement, see [
23].
In mathematics, differential inclusions relate to one or more functions and their derivatives. In applications, functions generally represent physical quantities, derivatives represent their rates of change, and differential inclusion defines the relationship between the two. Because these relationships are so common, differential equations play a prominent role in many disciplines, including engineering, physics, economics, and biology. The study of differential inclusions mainly consists of studying their solutions (the set of functions that satisfy the equation), and the properties of their solutions. The simplest differential inclusions can be solved by explicit formulas. However, many properties of solutions to particular differential inclusions may be determined without being exactly calculated. If a closed expression is not available for the solutions, the solutions may be numerically approximated using computers. Dynamical systems theory focuses on the qualitative analysis of systems described by differential equations and differential inclusions, while many numerical methods have been developed to determine solutions with a certain degree of precision.
Many of the basic laws of physics and chemistry can be formulated as differential equations. In biology and economics, differential equations are used to model the behavior of complex systems. The mathematical theory of differential equations developed first with the sciences in which the equations originated and where the results were put into practice. However, various problems which sometimes arise in quite distinct scientific fields may result in identical differential equations. Whenever this happens, the mathematical theory behind the equations can be seen as a unifying principle behind the various phenomena. For example, consider the propagation of light and sound in the atmosphere, and the waves on the surface of a pond. They can all be described by the same second-order partial differential equation, which is the wave equation, that allows us to think of light and sound as forms of waves, much like the familiar waves in water. Heat conduction, developed by Joseph Fourier, is governed by a second-order partial differential equation, the heat equation. It turns out that many diffusion processes, though apparently different, are described by the same equation; the Black–Scholes equation in finance, for example, is related to the heat equation [
24,
25]. In [
26], the authors were the first who developed the idea of the tripled fixed points. Karakaya et al. [
27] introduce tripled fixed points for a class of condensing operators in Banach spaces. In [
25], the authors studied the existence results for the following BVP.
      
      where 
 denotes the Caputo fractional derivatives (CFDs) of order 
, 
 are continuous functions, 
 is a cyclic permutation, and 
 In this work, motivated by [
28], we consider the following system of sequential fractional differential inclusions: 
      where 
 is a CFDs of order 
,
 are given continuous functions, 
 is the family of all non-empty subset of 
, 
 and 
.
The Caputo SFDEs with multi-point and integral boundary conditions discussed in this work are the most widely used Caputo fractional derivatives. The novelty and originality of this work is summarized by using Covitz and Nadler’s fixed point theorem and the non-linear alternative for Kakutani maps in showing the existence results for a tripled system of sequential fractional differential inclusions.
Preliminaries are introduced in the second section, main results are shown in the third section. Finally, in 
Section 4, we give some numerical examples to show the effectiveness of the obtained theoretical results.
  2. Preliminaries
This portion introduces basic fractional calculus concepts, definitions, and tentative results [
1,
2,
3].
Let  be a Banach space endowed with the norm . Then  is also a Banach space equipped with the norm 
Let  be a normed space and that , .
A multi-valued map  is
- (a)
 Convex valued if  is convex ;
- (b)
 Upper semi-continuous (U.S.C.) on  if, for each ; the set  is a non-empty closed subset of  and if, for each open set  of  containing , there exists an open neighborhood  of , such that ;
- (c)
 Lower semi-continuous (L.S.C.) if the set  is open for any open set  in ;
- (d)
 Completely continuous (C.C) if  is relatively compact (r.c) for every .
A map  of multi-valued is said to be measurable if, for every , the function  is measurable.
A multi-valued map  is said to be Caratheodory if
- (i)
  is measurable for each ;
- (ii)
  is U.S.C for almost all .
Further, a Caratheodory function  is called -Caratheodory if
- (i)
 For each , ∃∋ with  and for a.e. .
Lemma 1. Let  a closed convex subset of a Banach space  and  be an open subset of  with . In addition,  is an u.s.c compact map. Then either
 has fixed point in  or
∃ and , such that .
 Lemma 2  ([
29]). 
Let  be a completely continuous operator in Banach Space  and the set  is bounded. Then  has a fixed point in . Definition 1.  The fractional integral of order ψ with the lower limit zero for a function k is defined asprovided the right-hand side is point-wise defined on , where  is the gamma function, which is defined by   Definition 2.  The R-L fractional derivative of order  is defined aswhere the function k has absolutely continuous derivative up to order .  Definition 3. The Caputo derivative of order  for a function  can be written as Note that the CFDs of order  almost everywhere on  if .
 Next, we state and prove the auxiliary lemma, which will help us in constructing the existence results for our proposed system.
Lemma 3. Let  and . Then the solution of the linear fractional differential system,is given by    3. Multi-Valued System
Definition 4. A function  satisfying the boundary conditions and for which there , such that
 a.e. on  and
 With the help of Lemma 3, we define an operator 
 by
      
      
        
      
      
      
      
     
      and
      
For easy calculations, we set
      
Next, we define the operators  as follows:
Then, we define an operator 
 by
      
      and
      
  3.1. The Caratheodory Case
Our first result dealing with convex values , and  is proved via the Leray–Schauder non-linear alternative for multi-valued maps.
Theorem 1. Suppose that the following conditions are satisfied:
 are  Caratheodory and have convex values;
 There exist continuous non-decreasing functions  functions , such thatandfor each ;  there exists a number , such thatwhere  and  are given by (10). The tripled system has at least one solution on .  Proof.  Consider the operator 
 defined by (
11)–(
13). From 
, it follows that sets 
, 
 and 
 are non-empty for each 
. Then, for 
 for 
, we have
          
          and
          
          and
          
          where 
, and 
.
For the applicability of Leray–Schauder non-linear alternative we split our proof into several steps.
Claim 1. The operator 
 is convex. Let 
 Then there exist 
 such that, for each 
, we have
          
          and
          
 Let 
. Then, for each 
, we have 
          and
          
We deduce that  and  are convex valued, since  are convex valued. obviously, ,, and  hence .
Claim 2. We show that the operator 
 maps bounded sets into bounded sets in 
. Let 
, define 
 be a bounded set in 
. Then, there exist 
 and 
, such that
          
 Claim 3. We show the equi-continuity of the operator 
. Let 
 with 
. Then there exist 
,
, and 
, such that
          
          and,
          
 Therefore, the operator  is equi-continuous, based on Arzela–Ascoli  is completely continuous. We know that a completely continuous operator is upper semi-continuous if it has a closed graph. Thus, we need to prove that  has a closed graph.
Claim 4. We show that the operator 
 has closed graph. As it is known that a completely continuous operator is upper semi-continuous if it has a closed graph. For this we take 
, 
 and 
, then we need to show 
. Observe that 
 implies that exist 
, 
, and  
 such that
          
          and
          
 Let us consider the continuous linear operator 
 given by
          
          and
          
          and
          
From, we know that 
 is closed graph operator. Further, we have 
 for all 
n. Since 
, 
 it follows that 
 and 
, and 
, such that
          
          and
          
          that is, 
.
Exists with: let 
. this implies that the function 
, 
, and 
 exists with:
          
          and
          
          following the same arguments
          
          which implies that
          
In the light of 
 we can find 
 with 
. Consider
          
Here,  is completely continuous and upper semi-continuous. There is no  for some  depending on choosing of .
So, by the non-linear alternative of Leray–Schauder type, we conclude that 
 has it least one fixed point 
, this solution of problem (
1). By this, we finalize the proof.    □
   3.2. The Case of Libschitz
Here, we consider the situation where there are non-convex values in the multi valued maps of system (
1).
Consider the metric space  which is induced from the normed space , and consider  be given by  where  and 
So  is a metric space and  is a generalized one.
In the upcoming result, we take advantage of Covitz and Nadler’s fixed point theorem for multi-valued maps.
Theorem 2.   are such that , , and  are measurable for each 
andfor the majority of  and  with  and  for almost  hold, this implies the existence of solution for system (1) on  given that  Proof.  The sets , and  are non-empty for each  by assumption , so ,  and  have measurable selections. We now demonstrate that the operator  meets the criteria of Covitz and Nadler’s fixed point theorem.
We start by 
 for each 
. Let 
, such that 
 in 
. Then 
 and there exists 
, 
, and 
, such that
          
          and
          
          because of the compact values 
, 
, and 
, we take the sub-sequences to show that 
, 
 and 
 tends to 
, 
, and 
 in 
, respectively. Thus, 
, 
, and 
 for each 
 and that
          
          and
          
So 
, which guarantees that 
 is closed. After that, we prove the existence of 
, such that
          
Let 
 and 
 then there exist 
, 
, and 
 such that, ∀
, this gives
          
So, there 
, 
 and 
 such that
          
          and
          
Defined 
 by
          
          and
          
Since the multi-valued operators 
, 
 and 
 are measurable, there exist functions 
 which are a measurable selection for 
 and 
, 
, 
 such that, for a.e. 
, we have
          
          and
          
Thus
          
          likewise, by reversing the roles of 
 and 
, it is possible to obtain
          
In light of the assumption, 
 is a contraction. Therefore, according to Covitz and Nadler’s fixed point theorem, it has a fixed point 
 that is a solution to problem (
1). This concludes the proof.    □