Int. J. Anal. Appl. (2023), 21:55 Existence of Solutions via C-Class Functions in Ab-Metric Spaces With Applications N. Mangapathi1,3,∗, B. Srinuvasa Rao2, K.R.K. Rao3, M.I. Pasha1,3 1Department of Mathematics, B V Raju Institute of Technology, Narsapur, Medak-502313,Telangana, India 2Department of Mathematics, Dr.B.R.Ambedkar University, Srikakulam, Etcherla-532410, Andhra Pradesh, India 3Department of Mathematics, Gitam School of Science, GITAM Deemed to be University, Hyderabad, Rudraram-502329, Telangana, India ∗Corresponding author: nmp.maths@gmail.com Abstract. Using C-class functions, we demonstrate a few popular common coupled fixed point theo- rems on Ab-metric spaces and discuss some implications of the main findings. Additionally, we provide examples to illustrate the findings and their applications to both homotopy theory and integral equa- tions. 1. Introduction Fixed point theory plays a significant role in many parts of the development of nonlinear analysis. It has been applied to various fields of engineering and research. This research was inspired by recent work on the extension of the Banach contraction principle on Ab metric spaces, which was carried out by M. Ughade et al. [1] and studied various fixed point results on these spaces. In the further, N. Mlaiki et al. [2] and K. Ravibabu et al. [3], [4] and P. Naresh et al. [5] succeeded in deriving unique coupled common fixed point theorems in Ab-metric spaces. Sessa [6] began researching common fixed point theorems for weakly commuting pair of mappings in 1982. Later, in 1986, Jungck [7] expanded the idea of weakly commuting mappings to compatible mappings in metric spaces and proved compatible pair mappings commute on the sets of coincidence point of the involved mappings. When they commute at their coincidence sites, Jungck and Rhoades [8] Received: Mar. 23, 2023. 2020 Mathematics Subject Classification. 54H25, 47H10, 54E50. Key words and phrases. C-class function; ω-compatible mapping; Ab-completeness; coupled fixed points. https://doi.org/10.28924/2291-8639-21-2023-55 ISSN: 2291-8639 © 2023 the author(s). https://doi.org/10.28924/2291-8639-21-2023-55 2 Int. J. Anal. Appl. (2023), 21:55 introduced the idea of weak compatibility in 1998 and demonstrated that compatible mappings are weakly compatible but the reverse is not true. However, Khan et al. [9] first proposed the idea of modifying distance function, which is a control function that modifies the distance between two locations in a metric space. Ansari [10] presented the idea of C-class functions in 2014 and proved the unique fixed point theorems for certain contractive mappings with regard to the C-class functions, which started a lot of work in this field (See. [11], [12], [13], [14], [15], [16], [17]) The idea of coupled fixed point was first developed by Guo and Lakshmikantham [18] in 1987 . Later, employing a weak contractivity type assumption, Bhaskar and Lakshmikantham [19] developed a novel fixed point theorem for a mixed monotone mapping in a metric space driven with partial ordering. See study results in ( [20], [21], [22], [23], [24]) and related references for additional results on coupled fixed point outcomes. In the framework of Ab-metric spaces, the goal of the current study is to establish original common coupled fixed point theorems using C-class functions. Additionally, we may provide relevant applications for homotopy, integral equations, and appropriate examples. First we recall some basic results. 2. Preliminaries Definition 2.1. ( [1]) Let = be a non-empty set and b ≥ 1 be given real number. A mapping Ab : =n → [0,∞) is called an Ab-metric on = if and only if for all Υi,a ∈ = i = 1, 2, 3, ..n; the following conditions hold : (Ab1) Ab(Υ1, Υ2, ........, Υn−1, Υn) ≥ 0, (Ab2) Ab(Υ1, Υ2, ........, Υn−1, Υn) = 0 ⇔ Υ1 = Υ2 = · · · · · · = Υn−1 = Υn, (Ab3) Ab(Υ1, Υ2, ........, Υn−1, Υn) ≤ b   Ab (Υ1, Υ1, ........, (Υ1)n−1,a) +Ab (Υ2, Υ2, ........, (Υ2)n−1,a) + · · · · · · + Ab (Υn−1, Υn−1, ........, (Υn−1)n−1,a) +Ab (Υn, Υn, ........, (Υn)n−1,a)   Then the pair (=,Ab) is called an Ab-metric space. Remark 2.1. ( [1]) The class of Ab-metric spaces is actually larger than that of A-metric spaces, it should be emphasised. Each A-metric space is, in fact, a Ab-metric space with b = 1. The opposite isn’t always true, though. A n-dimensional Sb-metric space is also a Ab-metric space. As a result, a Ab-metric with n = 3 is a particular instance of a Sb-metric. The example below demonstrates that an Ab-metric on = need not be an A-metric on =. Example 2.1. ( [1]) Let = = [0, +∞), define Ab : =n → [0, +∞) as Ab (Υ1, Υ2, ........, Υn−1, Υn) = ∑n i=1 ∑ i 1. Int. J. Anal. Appl. (2023), 21:55 3 Definition 2.2. ( [1]) Let (=,Ab) be a Ab-metric space. Then, for Υ ∈=, r > 0 we defined the open ball BAb (Υ, r) and closed ball BAb [Υ, r] with center Υ and radius r as follows respectively: BAb (Υ, r) = {f∈= : Ab(f,f, · · · , (f)n−1, Υ) < r}, and BAb [Υ, r] = {f∈= : Ab(f,f, · · · , (f)n−1, Υ) ≤ r}. Lemma 2.1. ( [1]) In a Ab-metric space, we have (1) Ab(Υ, Υ, · · · , (Υ)n−1,f) ≤ bAb(f,f, · · · , (f)n−1, Υ); (2) Ab(Υ, Υ, · · · , (Υ)n−1,ð) ≤ b(n− 1)Ab(Υ, Υ, · · · , (Υ)n−1,f) + b2Ab(f,f, · · · , (f)n−1,ð). Definition 2.3. ( [1]) If (=,Ab) be a Ab-metric space. A sequence {Υk} in = is said to be: (1) Ab-Cauchy sequence if, for each � > 0, there exists n0 ∈ N such that Ab(Υk, Υk, · · · · · ·(Υk)n−1, Υm) < � for each m,k ≥ n0. (2) Ab-convergent to a point Υ ∈= if, for each � > 0, there exists a positive integer n0 such that Ab(Υk, Υk, · · · · · ·(Υk)n−1, Υ) < � for all n ≥ n0 and we denote by lim k→∞ Υk = Υ. (3) If every Ab-Cauchy sequence is Ab-convergent in =, then the Ab-metric space (=,Ab) is said to be complete. Definition 2.4. [10] A continuous mapping Γ : [0, +∞) × [0. + ∞) → R is called a C-class function if for all s∗,t∗ ∈ [0,∞), (a) Γ(s∗,t∗) ≤ s; (b) Γ(s∗,t∗) = s∗ implies that either s∗ = 0 or t∗ = 0. The family of all C-class functions is denoted by C. Example 2.2. [10] Each of the functions Γ : [0, +∞) × [0. + ∞) → R defined below are elements of C. (a) Γ(s∗,t∗) = s? − t?; (b) Γ(s∗,t∗) = ms∗ where m ∈ (0, 1). (c) Γ(s∗,t∗) = s ∗ (1+t?)r where r ∈ (0,∞). (d) Γ(s∗,t∗) = s?η(s?) where η : [0,∞) → [0,∞) is continuous function. (e) Γ(s∗,t∗) = s? −ϕ(s?) for all s∗,t∗ ∈ [0, +∞) where, the continuous function ϕ : [0,∞) → [0,∞) such that ϕ(s?) = 0 ⇔ s? = 0. (f ) Γ(s∗,t∗) = sΩ(s?,t?) for all s∗,t∗ ∈ [0, +∞) where, the continuous function Ω : [0,∞)2 → [0,∞) such that Ω(s?,t?) < 1. Definition 2.5. [9] A function θ? : [0,∞) → [0,∞) is called an altering distance function if the following properties are satisfied: (a) θ? is nondecreasing and continuous; 4 Int. J. Anal. Appl. (2023), 21:55 (b) θ?(t) = 0 if and only if t = 0. Here Θ represents the family of all altering distance functions. We must take the following into consideration in order to get our outcomes. 3. Main Results Definition 3.1. Let (=,Ab) be a Ab-metric spaces and suppose Ω : =2 → = be a mapping. If Ω (℘,$) = ℘, Ω ($,℘) = $ for ℘,$ ∈= then (℘,$) is called a coupled fixed point of Ω. Definition 3.2. Let (=,Ab) be a Ab-metric spaces and suppose Ω : =2 → = and Λ : = → = be two mappings. An element (℘,$) is said to be a coupled coincident point of Ω and Λ if F (℘,$) = Λ℘, Ω ($,℘) = Λ$ Definition 3.3. Let (=,Ab) be a Ab-metric spaces and suppose Ω : =2 → =, Λ : = → = be two mappings. An element (℘,$) is said to be a coupled common point of Ω and Λ if Ω (℘,$) = Λ℘ = ℘, Ω ($,℘) = Λ$ = $, Definition 3.4. Let (=,Ab) be a Ab-metric space. (a) A pair (Ω, Λ) is called weakly compatible if Λ(Ω(℘,$)) = Ω(Λ℘, Λ$) whenever for all ℘,$ ∈= such that F (℘,$) = Λ℘, Ω ($,℘) = Λ$ (b) A pair (Ω, Λ) is called compatible if lim p→∞ Ab(ΛΩ(ıp, p), ΛΩ(ıp, p) · · · , Ω(Λıp, Λp)) = lim p→∞ Ab(ΛΩ(p, ıp), ΛΩ(p, ıp) · · · , Ω(Λp, Λıp)) = 0 wherever {ıp},{p} are sequences in =, such that lim p→∞ Ω(ıp, p) = Λıp = ı and lim p→∞ Ω(p, ıp) = Λp = . Lemma 3.1. If the pair (Ω, Λ) of mappings on the Ab-metric space (=,Ab) is compatible, then it is weakly compatible. The converse does not hold. Proof. Let Ω(i, j) = Λi and Ω(j, i) = Λj for some i, j ∈=. we have to prove that ΛΩ(i, j) = Ω(Λi, Λj) and ΛΩ(j, i) = Ω(Λj, Λi). Put ıp = i and p = j for every p ∈ N. we have Ω(ıp, p) = Λıp → Λi and Ω(p, ıp) = Λp → Λj. Since (Ω, Λ) is compatible lim p→∞ Ab(ΛΩ(ıp, p), ΛΩ(ıp, p) · · · , Ω(Λıp, Λp)) = lim p→∞ Ab(ΛΩ(p, ıp), ΛΩ(p, ıp) · · · , Ω(Λp, Λıp)) = 0 Therefore, ΛΩ(i, j) = Ω(Λi, Λj) and ΛΩ(j, i) = Ω(Λj, Λi) and hence the pair (Ω, Λ) is weakly compat- ible. However, the opposite need not be the case. For example, Let = = [0, +∞), define Ab : =n → [0, +∞) as Ab (Υ1, Υ2, ........, Υn−1, Υn) = ∑n i=1 ∑ i 1. Int. J. Anal. Appl. (2023), 21:55 5 Define two mappings Ω : =2 → = by Ω(i, j) = { 6i−3j+6n−3 6n for i, j ∈ [0, 1 2 ) n 4 for i, j ∈ [1 2 ,∞) and Λ : = → = by Λ(i) = { 9i+6n−6 6n for i ∈ [0, 1 2 ) n 4 for i ∈ [1 2 ,∞) Now we define the two sequences {ıp},{p} as ıp = 1p and p = 1 + 1 p , then Ω(ıp, p) = 3 p +6n−6 6n → n−1 n as p → ∞ and Λ(ıp) = 9 p +6n−6 6n → n−1 n as p → ∞, also Ω(p, ıp) = 3 p +6n+3 6n → 2n+1 2n as p → ∞ and Λ(p) = 9 p +6n+3 6n → 2n+1 2n as p →∞. But lim p→∞ Ab(ΛΩ(ıp, p), ΛΩ(ıp, p) · · · , Ω(Λıp, Λp)) = lim p→∞ Ab( 27 p + 36n2 + 18n− 54 36n2 , 27 p + 36n2 + 18n− 54 36n2 · · · , 27 p + 36n2 − 45 36n2 ) = (n− 1)| 2n− 1 4n2 |2 6= 0, if n = 2. and lim p→∞ Ab(ΛΩ(p, ıp), ΛΩ(p, ıp) · · · , Ω(Λp, Λıp)) = lim p→∞ Ab( 27 p + 36n2 + 18n + 27 36n2 , 27 p + 36n2 + 18n + 27 36n2 · · · , 27 p + 36n2 + 36 36n2 ) = (n− 1)| 2n− 1 4n2 |2 6= 0, if n = 2. Thus the pair (Ω, Λ) is not compatible. Also,Then for any i, j ∈ [1 2 ,∞), (n 4 , n 4 )is a coupled coincidence point of Ω and Λ it is namely that i = j = n 4 , Ω(i, j) = 7 8 = Λi and Ω(j, i) = 7 8 = Λj for n = 2 and λΩ(i, j) = Ω(Λi, Λj), λΩ(j, i) = Ω(Λj, Λi), showing that Ω, Λ are weakly compatible maps on =. � Theorem 3.1. Let (=,Ab) be a complete Ab-metric space. Suppose T : =2 →= and f : =→= be a two mappings satisfying the following: η? ( 2b2Ab(T (ı, ),T (ı, ), · · · ,T (ð,f)) ) ≤ Γ (η? (Ab(f ı, f ı, · · · , fð)) ,θ? (Ab(f , f , · · · , ff))) (3.1) for all ı, ,ð,f∈=, where η?,θ? ∈ Θ and Γ ∈ C a) T (=2) ⊆ f (=); b) pair (T,f ) is compatible; c) f is continuous. Then there is a unique common coupled fixed point of T and f in =. Proof. Let ı0, 0 ∈= be arbitrary, and from (a), we construct the sequences {ıp} ,{p} , in = as T (ıp, p) = f ıp+1 = ℵp, T (p, ıp) = f p+1 = Υp, where p = 0, 1, 2, . . . . 6 Int. J. Anal. Appl. (2023), 21:55 Now from (3.1), we have η? ( 2b2Ab(ℵ1,ℵ1, · · · ,ℵ2) ) = η? ( 2b2Ab(T (ı1, 1),T (ı1, 1), · · · ,T (ı2, 2)) ) ≤ Γ (η? (Ab(f ı1, f ı1, · · · , f ı2)) ,θ? (Ab(f 1, f 1, · · · , f 2))) ≤ η? (Ab(f ı1, f ı1, · · · , f ı2)) ≤ η? (Ab(ℵ0,ℵ0, · · · ,ℵ1)) By the definition of η?, we have that Ab(ℵ1,ℵ1, · · · ,ℵ2) ≤ 1 2b2 Ab(ℵ0,ℵ0, · · · ,ℵ1). Also η? ( 2b2Ab(ℵ2,ℵ2, · · · ,ℵ3) ) = η? ( 2b2Ab(T (ı2, 2),T (2, 2), · · · ,T (ı3, 3)) ) ≤ Γ (η? (Ab(f ı2, f ı2, · · · , f ı3)) ,θ? (Ab(f 2, f 2, · · · , f 3))) ≤ η? (Ab(f ı2, f ı2, · · · , f ı3)) ≤ η? (Ab(ℵ1,ℵ1, · · · ,ℵ2)) By the definition of η?, we have that Ab(ℵ2,ℵ2, · · · ,ℵ3) ≤ 1 2b2 Ab(ℵ1,ℵ1, · · · ,ℵ2) ≤ 1 (4b2)2 Ab(ℵ0,ℵ0, · · · ,ℵ1) Continuing this process, we can conclude that Ab(ℵp,ℵp, · · · ,ℵp+1) ≤ 1 (2b2)p Ab(ℵ0,ℵ0, · · · ,ℵ1) → 0 as p →∞. that is lim p→∞ Ab(ℵp,ℵp, · · · ,ℵp+1) = 0. Similarly, we can prove that lim p→∞ Ab(Υp, Υp, · · · , Υp+1) = 0. Now for q > p, by use of (Ab3), we have Ab (ℵp,ℵp, · · · ,ℵn−1,ℵq) ≤ b   Ab (ℵp,ℵp, ........, (ℵp)n−1,ℵp+1) +Ab (ℵp,ℵp, ........, (ℵp)n−1,ℵp+1) + · · · · · · + Ab (ℵp,ℵp, ........, (ℵp)n−1,ℵp+1) +Ab (ℵq,ℵq, ........, (ℵq)n−1,ℵp+1)   Int. J. Anal. Appl. (2023), 21:55 7 ≤ b(n− 1)Ab (ℵp,ℵp, ........, (ℵp)n−1,ℵp+1) +bAb (ℵq,ℵq, ........, (ℵq)n−1,ℵp+1) ≤ b(n− 1)Ab (ℵp,ℵp, ........, (ℵp)n−1,ℵp+1) +b2Ab (ℵp+1,ℵp+1, ........, (ℵp+1)n−1,ℵq) ≤ b(n− 1)Ab (ℵp,ℵp, ........, (ℵp)n−1,ℵp+1) +b3(n− 1)Ab (ℵp+1,ℵp+1, ........, (ℵp+1)n−1,ℵp+2) +b4Ab (ℵp+2,ℵp+2, ........, (ℵp+2)n−1,ℵq) ≤ b(n− 1)Ab (ℵp,ℵp, ........, (ℵp)n−1,ℵp+1) +b3(n− 1)Ab (ℵp+1,ℵp+1, ........, (ℵp+1)n−1,ℵp+2) +b5(n− 1)Ab (ℵp+2,ℵp+2, ........, (ℵp+2)n−1,ℵp+3) +b7(n− 1)Ab (ℵp+3,ℵp+3, ........, (ℵp+3)n−1,ℵp+4) + . . . + b2q−2p−2(n− 1)Ab (ℵq−2,ℵq−2, ........, (ℵq−2)n−1,ℵq−1) +b2q−2p−3Ab (ℵq−1,ℵq−1, ........, (ℵq−1)n−1,ℵq) ≤ (n− 1) ( b 1 (2b2)p + b3 1 (2b2)p+1 + b5 1 (2b2)p+2 + . . . + b2q−2p−2 1 (2b2)q−2 ) Ab (ℵ0,ℵ0, · · · ,ℵ1) +b2q−2p−3 1 (2b2)q−1 Ab (ℵ0,ℵ0, · · · ,ℵ1) ≤ (n− 1)b 1 (2b2)p ( 1 + b2 1 2b2 + b4( 1 2b2 )2 + . . . + b2q−2p−4( 1 2b2 )q−p−2 ) Ab (ℵ0,ℵ0, · · · ,ℵ1) +b2q−2p−3( 1 2b2 )q−p−1Ab (ℵ0,ℵ0, · · · ,ℵ1) ≤ (n− 1)b 1 (2b2)p ( 1 + 1 2 + 1 22 + . . . + 1 2q−p−2 + · · · ) Ab (ℵ0,ℵ0, · · · ,ℵ1) ≤ 2(n− 1)b 1 (2b2)p Ab (ℵ0,ℵ0, · · · ,ℵ1) → 0 as p,q →∞. Hence {ℵp} is a Cauchy sequence in = . We can also demonstrate that {Υp}, is Cauchy sequence in =. Therefore, lim p,q→∞ Ab(ℵp,ℵp, · · · ,ℵq) = 0, and lim p,q→∞ Ab(Υp, Υp, · · · , Υq) = 0. Since (=,Ab) is complete, there exist ℵ, Υ ∈= such that lim p→∞ ℵp = lim p→∞ T (ıp, p) = lim p→∞ f ıp+1 = ℵ lim p→∞ Υp = lim p→∞ T (p, ıp) = lim p→∞ f p+1 = Υ. Since f : =→= is continuous lim p→∞ f 2ıp+1 = fℵ and lim p→∞ f T (ıp, p) = fℵ 8 Int. J. Anal. Appl. (2023), 21:55 lim p→∞ f 2p+1 = f Υ and lim p→∞ f T (p, ıp) = f Υ Since {T,f} is compatible, we have F (f ıp, f p) → fℵ and F (f p, f ıp) → f Υ lim p→∞ Ab(T (f ıp, f p),T (f ıp, f p) · · · , f T (ıp, p)) = 0. (3.2) lim p→∞ Ab(T (f p, f ıp),T (f p, f ıp) · · · , f T (p, ıp)) = 0. (3.3) Now, we prove that fℵ = T (ℵ, Υ) and f Υ = T (Υ,ℵ). For all p ≥ 0, we have Ab (fℵ, fℵ, · · · , (fℵ)n−1,T (f ıp, f p)) ≤ b ( (n− 1)Ab (fℵ, fℵ, ........, (fℵ)n−1, f T (ıp, p)) +Ab (f T (ıp, p), f T (ıp, p), ........, (f T (ıp, p))n−1,T (f ıp, f p)) ) ≤ (n− 1)bAb (fℵ, fℵ, ........, (fℵ)n−1, f T (ıp, p)) +b2Ab (T (f ıp, f p),T (f ıp, f p), ........, (T (f ıp, f p))n−1, f T (ıp, p)) On taking limits as p →∞ and from (3.2 ) we get Ab (fℵ, fℵ, · · · , (fℵ)n−1,T (ℵ, Υ)) = 0. Similarly it is easy to see that Ab (f Υ, f Υ, · · · , (f Υ)n−1,T (Υ,ℵ)) = 0. Thus, T (ℵ, Υ) = fℵ and T (Υ,ℵ) = f Υ. Hence (ℵ, Υ) is a coupled coincidence point of T and f . Now we prove that fℵ = ℵ and f Υ = Υ. Now consider η? ( 2b2Ab (fℵ, fℵ, · · · , (fℵ)n−1,ℵp) ) = η? ( 2b2Ab (T (ℵ, Υ),T (ℵ, Υ), · · · , (T (ℵ, Υ))n−1,T (ıp, p)) ) ≤ Γ (η? (Ab(fℵ, fℵ, · · · , f ıp)) ,θ? (Ab(f Υ, f Υ, · · · , f ))) ≤ η? (Ab(fℵ, fℵ, · · · , f ıp)) By the definition of η?, we have Ab (fℵ, fℵ, · · · , (fℵ)n−1,ℵp) ≤ 1 2b2 Ab(fℵ, fℵ, · · · , f ıp) Letting p → ∞ , we get Ab (fℵ, fℵ, · · · , (fℵ)n−1,ℵ) ≤ 12b2Ab(fℵ, fℵ, · · · ,ℵ) which implies that fℵ = ℵ. Similarly, we can prove f Υ = Υ. Therefore, T (ℵ, Υ) = fℵ = ℵ and T (Υ,ℵ) = f Υ = Υ. Thus,(ℵ, Υ) is a common coupled point of T and f . In order to demonstrate uniqueness, we first assume that (ℵ?, Υ?) is a another coupled common fixed point of T and f . Now η? ( 2b2Ab (ℵ,ℵ, · · · , (ℵ)n−1,ℵ?) ) = η? ( 2b2Ab (T (ℵ, Υ),T (ℵ, Υ), · · · , (T (ℵ, Υ))n−1,T (ℵ?, Υ?)) ) ≤ Γ (η? (Ab(fℵ, fℵ, · · · , fℵ?)) ,θ? (Ab(f Υ, f Υ, · · · , f Υ?))) ≤ η? (Ab(fℵ, fℵ, · · · , fℵ?)) ≤ η? (Ab(ℵ,ℵ, · · · ,ℵ?)) Int. J. Anal. Appl. (2023), 21:55 9 By the definition of η?, we have Ab(ℵ,ℵ, · · · ,ℵ?) ≤ 12b2Ab(ℵ,ℵ, · · · ,ℵ ?) Therefore, Ab(ℵ,ℵ, · · · ,ℵ?) = 0 implies ℵ = ℵ?. Similarly, we can shows that Υ = Υ?. Thus,(ℵ, Υ) is a unique common coupled point of T and f . Finally, we will show ℵ = Υ. η? ( 2b2Ab (ℵ,ℵ, · · · , (ℵ)n−1, Υ) ) = η? ( 2b2Ab (T (ℵ, Υ),T (ℵ, Υ), · · · , (T (ℵ, Υ))n−1,T (Υ,ℵ)) ) ≤ Γ (η? (Ab(fℵ, fℵ, · · · , f Υ)) ,θ? (Ab(f Υ, f Υ, · · · , fℵ))) ≤ η? (Ab(fℵ, fℵ, · · · , f Υ)) ≤ η? (Ab(ℵ,ℵ, · · · , Υ)) By the definition of η?, we have Ab(ℵ,ℵ, · · · , Υ) ≤ 12b2Ab(ℵ,ℵ, · · · , Υ). Therefore, Ab(ℵ,ℵ, · · · , Υ) = 0 implies ℵ = Υ. Thus,(ℵ,ℵ) is a common fixed point of T and f . � Theorem 3.2. Let (=,Ab) be a complete Ab-metric space. Suppose T : =2 →= and f : =→= be a two mappings satisfying the following: η? ( 2b2Ab(T (ı, ),T (ı, ), · · · ,T (ð,f)) ) ≤ Γ (η? (Ab(f ı, f ı, · · · , fð)) ,θ? (Ab(f , f , · · · , ff))) (3.4) for all ı, ,ð,f∈=, where η?,θ? ∈ Θ and Γ ∈ C a) T (=2) ⊆ f (=); b) pair (T,f ) is weakly compatible; c) f (=) is closed in =. Then there is a unique common coupled fixed point of T and f in =. Proof. Let ı0, 0 ∈= and from Theorem 3.1, we construct the sequences {ℵp} ,{Υp} in = are Cauchy sequences. Since (=,Ab) is complete, {ℵp} ,{Υp} are convergent as follows lim p→∞ ℵp = lim p→∞ T (ıp, p) = lim p→∞ f ıp+1 = ℵ lim p→∞ Υp = lim p→∞ T (p, ıp) = lim p→∞ f p+1 = Υ. Since f (=) is closed in (=,Ab), so {ℵp} ,{Υp} ⊆ f (=) are converges in the complete Ab- metric spaces (=,Ab), therefore, there exist ℵ, Υ ∈ f (=) with lim p→∞ ℵp+1 = ℵ lim p→∞ Υp+1 = Υ Since f : = → = and ℵ, Υ ∈ f (=), there exist f,℘ ∈ = such that ff = ℵ and f ℘ = Υ. We claim that T (f,℘) = ℵ and T (℘,f) = Υ. By using (3.4), we have η? ( 2b2Ab (T (ıp, p),T (ıp, p), · · · , (T (ıp, p))n−1,T (f,℘)) ) ≤ Γ (η? (Ab(f ıp, f ıp, · · · , ff)) ,θ? (Ab(f p, f p, · · · , f ℘))) ≤ η? (Ab(f ıp, f ıp, · · · , ff)) By the definition of η?, Ab (T (ıp, p),T (ıp, p), · · · , (T (ıp, p))n−1,T (f,℘)) ≤ 12b2Ab(f ıp, f ıp, · · · , ff) 10 Int. J. Anal. Appl. (2023), 21:55 Letting p →∞, it yields that lim p→∞ Ab (T (ıp, p),T (ıp, p), · · · , (T (ıp, p))n−1,T (f,℘)) ≤ lim p→∞ 1 2b2 Ab(f ıp, f ıp, · · · , ff) = 0. It follows that Ab (ℵ,ℵ, · · · , (ℵ)n−1,T (f,℘)) = 0 implies that T (f,℘) = ℵ. Similarly, we can prove T (℘,f) = Υ. Hence, T (f,℘) = ℵ = ff and T (℘,f) = Υ = f ℘. Since {T,f} is weakly compatible pair, we have T (ℵ, Υ) = fℵ and T (Υ,ℵ) = f Υ. Now we shall prove that fℵ = ℵ and f Υ = Υ. By using (3.4), we have η? ( 2b2Ab (fℵ, fℵ, · · · , (fℵ)n−1,ℵp) ) = η? ( 2b2Ab (T (ℵ, Υ),T (ℵ, Υ), · · · , (T (ℵ, Υ))n−1,T (ıp, p)) ) ≤ Γ (η? (Ab(fℵ, fℵ, · · · , f ıp)) ,θ? (Ab(f Υ, f Υ, · · · , f p))) ≤ η? (Ab(fℵ, fℵ, · · · , f ıp)) By the definition of η?, Ab (fℵ, fℵ, · · · , (fℵ)n−1,ℵp) ≤ 12b2Ab(fℵ, fℵ, · · · , f ıp) Letting p → ∞, it yields that Ab (fℵ, fℵ, · · · , (fℵ)n−1,ℵ) ≤ 12b2Ab(fℵ, fℵ, · · · ,ℵ), which possible holds only, Ab (fℵ, fℵ, · · · , (fℵ)n−1,ℵ) = 0 implies that fℵ = ℵ. Similarly, we shall show f Υ = Υ. It follows that T (ℵ, Υ) = fℵ = ℵ and T (Υ,ℵ) = f Υ = Υ. Therefore, the common coupled fixed point of T and f is (ℵ, Υ). It is simple to demonstrate the connected fixed point’s uniqueness and the common fixed point’s uniqueness of T and f , just like in the proof of Theorem 3.1. � Corollary 3.1. Let (=,Ab) be a complete Ab-metric space. Suppose a mapping T : =2 → = be satisfies: η? ( 2b2Ab(T (ı, ),T (ı, ), · · · ,T (ð,f)) ) ≤ Γ (η? (Ab(ı, ı, · · · ,ð)) ,θ? (Ab(, , · · · ,f))) for all ı, ,ð,f∈=, where η?,θ? ∈ Θ and Γ ∈ C. Then T has a unique coupled fixed point in =. Example 3.1. Let = = [0, +∞), define Ab : =n → [0, +∞) as Ab (℘1,℘2, ........,℘n−1,℘n) = ∑n i=1 ∑ i p, by use of (Ab3), we have Ab (℘p,℘p, · · · ,℘n−1,℘q) ≤ b(n− 1)Ab (℘p,℘p, ........, (℘p)n−1,℘p+1) +b2Ab (℘p+1,℘p+1, ........, (℘p+1)n−1,℘q) ≤ b(n− 1)Ab (℘p,℘p, ........, (℘p)n−1,℘p+1) +b3(n− 1)Ab (℘p+1,℘p+1, ........, (℘p+1)n−1,℘p+2) +b4Ab (℘p+2,℘p+2, ........, (℘p+2)n−1,℘q) ≤ b(n− 1)Ab (℘p,℘p, ........, (℘p)n−1,℘p+1) +b3(n− 1)Ab (℘p+1,℘p+1, ........, (℘p+1)n−1,℘p+2) +b5(n− 1)Ab (℘p+2,℘p+2, ........, (℘p+2)n−1,℘p+3) +b7(n− 1)Ab (℘p+3,℘p+3, ........, (℘p+3)n−1,℘p+4) + . . . + b2q−2p−2(n− 1)Ab (℘q−2,℘q−2, ........, (℘q−2)n−1,℘q−1) +b2q−2p−3Ab (℘q−1,℘q−1, ........, (℘q−1)n−1,℘q) → 0 as p,q →∞. Hence {℘p} is a Cauchy sequence in Ab metric spaces (=,Ab).Similarly, we may demonstrate that the Cauchy sequence in (=,Ab) is {$p} and by the fact that (=,Ab) is complete, there exist u,v ∈= with lim p→∞ ℘p+1 = u lim p→∞ ℘p lim p→∞ $p+1 = v = lim p→∞ $p We have η? ( 2b2Ab (u,u, · · · ,Hb(u,v,s)) ) = lim p→∞ η? ( 2b2Ab (Hb(℘p,$p,s),Hb(℘p,$p,s), · · · ,Hb(u,v,s)) ) ≤ lim n→∞ Γ (η? (Ab(℘p,℘p, · · · ,u)) ,θ? (Ab($p,$p, · · · ,v))) ≤ lim n→∞ η? (Ab(℘p,℘p, · · · ,u)) = 0 14 Int. J. Anal. Appl. (2023), 21:55 It follows thatHb(u,v,s) = u. Similarly, we can proveHb(v,u,s) = v. Thus s ∈=. Hence= is closed in [0, 1]. Let s0 ∈ =, then there exist ℘0,$0 ∈ V with ℘0 = Hb(℘0,$0,s0), $0 = Hb($0,℘0,s0). Since V is open, then there exist r > 0 such that BAb (℘0, r) ⊆ V . Choose s ∈ (s0−�,s0+�) such that |s − s0| ≤ 1Mp < � 2 , then for ℘ ∈ BAb (℘0, r) = {℘ ∈=/Ab(℘,℘, · · · ,℘0) ≤ r + Ab(℘0,℘0, · · · ,℘0)}. Now we have Ab (Hb(℘,$,s),Hb(℘,$,s), · · · ,℘0) = Ab (Hb(℘,$,s),Hb(℘,$,s), · · · ,Hb(℘0,$0,s0)) ≤ (n− 1)bAb (Hb(℘,$,s),Hb(℘,$,s), · · · ,Hb(℘,$,s0)) +b2Ab (Hb(℘,$,s0),Hb(℘,$,s0), · · · ,Hb(℘0,$0,s0)) ≤ b(n− 1)M|s − s0| + b2Ab (Hb(℘,$,s0),Hb(℘,$,s0), · · · ,Hb(℘0,$0,s0)) ≤ b(n− 1) 1 Mp−1 + b2Ab (Hb(℘,$,s0),Hb(℘,$,s0), · · · ,Hb(℘0,$0,s0)) Letting p →∞, we obtain Ab (Hb(℘,$,s),Hb(℘,$,s), · · · ,℘0) ≤ b2Ab (Hb(℘,$,s0),Hb(℘,$,s0), · · · ,Hb(℘0,$0,s0)) Since η?,θ? are continuous and non-decreasing, we obtain η? (Ab (Hb(℘,$,s),Hb(℘,$,s), · · · ,℘0)) ≤ η? ( 2b2Ab (Hb(℘,$,s0),Hb(℘,$,s0), · · · ,Hb(℘0,$0,s0)) ) ≤ Γ (η?(Ab(℘,℘, · · · ,℘0)),θ?(Ab($,$, · · · ,$0))) ≤ η?(Ab(℘,℘, · · · ,℘0)) Since η? is non-decreasing, we have Ab (Hb(℘,$,s),Hb(℘,$,s), · · · ,℘0) ≤ Ab(℘,℘, · · · ,℘0) ≤ r + Ab(℘0,℘0, · · · ,℘0). Similarly, we can prove, Ab (Hb($,℘,s),Hb($,℘,s), · · · ,$0) ≤ r + Ab($0,$0, · · · ,$0). Thus for each fixed s ∈ (s0 − �,s0 + �), Hb(.,s) : BAb (℘0, r) → BAb (℘0, r), Hb(.,s) : BAb ($0, r) → BAb ($0, r). All of the Theorem 5.1’s requirements are then met. Accord- ingly, we deduce that Hb(.,s) has a coupled fixed point in V 2 . But it has to be in V 2. Since (τ0) is true. The result is that s ∈ = for any s ∈ (s0 − �,s0 + �). Because of this, (s0 − �,s0 + �) ⊆ =. In [0, 1], = is obviously open. We follow the same approach for the opposite inference. � Conclusion: This paper wraps up a few applications to integral equations and homotopy theory using coupled fixed point theorems for C-class functions in the framework of Ab-metric spaces. Int. J. Anal. Appl. (2023), 21:55 15 Conflicts of Interest: The authors declare that there are no conflicts of interest regarding the publi- cation of this paper. References [1] M. Ughade, D. Turkoglu, S.R. Singh, et al. Some Fixed Point Theorems in Ab-Metric Space, Br. J. Math. Comput. Sci. 19 (2016), 1-24. [2] N. Mlaiki, Y. Rohen, Some Coupled Fixed Point Theorems in Partially Ordered Ab-Metric Space, J. Nonlinear Sci. Appl. 10 (2017), 1731?1743. https://doi.org/10.22436/jnsa.010.04.35. [3] R. Konchada, S.R. Chindirala, R.N. Chappa, A Novel Coupled Fixed Point Results Pertinent to Ab-Metric Spaces With Application to Integral Equations, Math. Anal. Contemp. Appl. 4 (2022), 63-83. https://doi.org/10. 30495/maca.2022.1949822.1046. [4] K. Ravibabu, C.S. Rao, C.R. Naidu, Applications to Integral Equations with Coupled Fixed Point Theorems in Ab-Metric Space, Thai J. Math. Spec. Iss. (2018), 148-167. [5] P. Naresh, G.U. Reddy, B.S. Rao, Existence Suzuki Type Fixed Point Results in Ab-Metric Spaces With Application, Int. J. Anal. Appl. 20 (2022), 67. https://doi.org/10.28924/2291-8639-20-2022-67. [6] S. Sessa, On a Weak Commutativity Condition of Mappings in Fixed Point Considerations, Publ. l’Inst. Math. 32 (1982), 149-153. http://eudml.org/doc/254762. [7] G. Jungck, Compatible Mappings and Common Fixed Points, Int. J. Math. Math. Sci. 9 (1986), 771-779. https: //doi.org/10.1155/s0161171286000935. [8] G. Jungck, B.E. Rhoades, Fixed Point for Set Valued Functions Without Continuity, Indian J. Pure Appl. Math. 29 (1998), 227-238. [9] M.S. Khan, M. Swaleh, S. Sessa, Fixed Point Theorems by Altering Distances Between the Points, Bull. Austral. Math. Soc. 30 (1984), 1-9. https://doi.org/10.1017/s0004972700001659. [10] A.H. Ansari, Note on ϕ−ψ-Contractive Type Mappings and Related Fixed Point, in: The 2nd Regional Conference on Mathematics and Applications, Payame Noor University, 2014. [11] A.H. Ansari, A. Kaewcharoen, C-Class Functions and Fixed Point Theorems for Generalized ℵ−η −ψ −ϕ−F- Contraction Type Mappings in ℵ − η-Complete Metric Spaces, J. Nonlinear Sci. Appl. 9 (2016), 4177-4190. https://doi.org/10.22436/jnsa.009.06.60. [12] H. Huang, G. Deng, S. Radenovic, Fixed Point Theorems for C-Class Functions in b-Metric Spaces and Applications, J. Nonlinear Sci. Appl. 10 (2017), 5853-5868. https://doi.org/10.22436/jnsa.010.11.23. [13] A.H. Ansari, W. Shatanawi, A. Kurdi, G. Maniu, Best Proximity Points in Complete Metric Spaces With (P)- Property via C-Class Functions, J. Math. Anal. 7 (2016), 54-67. [14] V. Ozturk, A.H. Ansari, Common Fixed Point Theorems for Mappings Satisfying (E.A)-Property via C-Class Func- tions in b-Metric Spaces, Appl. Gen. Topol. 18 (2017), 45-52. https://doi.org/10.4995/agt.2017.4573. [15] T. Hamaizia, Common Fixed Point Theorems Involving C-Class Functions in Partial Metric Spaces, Sohag J. Math. 8 (2021), 23-28. https://doi.org/10.18576/sjm/080103. [16] G.S. Saluja, Common Fixed Point Theorems on S-Metric Spaces Via C-Class Functions, Int. J. Math. Comb. 3 (2022), 21-37. [17] W. Shatanawi, M. Postolache, A.H. Ansari, W. Kassab, Common Fixed Points of Dominating and Weak Annihilators in Ordered Metric Spaces via C-Class Functions, J. Math. Anal. 8 (2017), 54-68. [18] D. Guo, V. Lakshmikantham, Coupled Fixed Points of Nonlinear Operators With Applications, Nonlinear Anal.: Theory Methods Appl. 11 (1987), 623-632. https://doi.org/10.1016/0362-546x(87)90077-0. [19] T.G. Bhaskar, V. Lakshmikantham, Fixed Point Theorems in Partially Ordered Metric Spaces and Applications, Nonlinear Anal.: Theory Methods Appl. 65 (2006), 1379-1393. https://doi.org/10.1016/j.na.2005.10.017. https://doi.org/10.22436/jnsa.010.04.35 https://doi.org/10.30495/maca.2022.1949822.1046 https://doi.org/10.30495/maca.2022.1949822.1046 https://doi.org/10.28924/2291-8639-20-2022-67 http://eudml.org/doc/254762 https://doi.org/10.1155/s0161171286000935 https://doi.org/10.1155/s0161171286000935 https://doi.org/10.1017/s0004972700001659 https://doi.org/10.22436/jnsa.009.06.60 https://doi.org/10.22436/jnsa.010.11.23 https://doi.org/10.4995/agt.2017.4573 https://doi.org/10.18576/sjm/080103 https://doi.org/10.1016/0362-546x(87)90077-0 https://doi.org/10.1016/j.na.2005.10.017 16 Int. J. Anal. Appl. (2023), 21:55 [20] M. Abbas, M.A. Khan, S. Radenovic, Common Coupled Fixed Point Theorems in Cone Metric Spaces for ω- Compatible Mappings, Appl. Math. Comput. 217 (2010), 195-202. https://doi.org/10.1016/j.amc.2010.05. 042. [21] A. Aghajani, M. Abbas, E.P. Kallehbasti, Coupled Fixed Point Theorems in Partially Ordered Metric Spaces and Application, Math. Commun. 17 (2012), 497-509. https://hrcak.srce.hr/93280. [22] E. Karapinar, Coupled Fixed Point on Cone Metric Spaces, Gazi Univ. J. Sci. 1 (2011), 51-58. [23] M. Abbas, B. Ali, Y.I. Suleiman, Generalized Coupled Common Fixed Point Results in Partially Ordered A-Metric Spaces, Fixed point theory Appl. 2015 (2015), 64. [24] W. Long, B.E. Rhoades, M. Rajovic, Coupled Coincidence Points for Two Mappings in Metric Spaces and Cone Metric Spaces, Fixed Point Theory Appl. 2012 (2012), 66. https://doi.org/10.1186/1687-1812-2012-66. https://doi.org/10.1016/j.amc.2010.05.042 https://doi.org/10.1016/j.amc.2010.05.042 https://hrcak.srce.hr/93280 https://doi.org/10.1186/1687-1812-2012-66 1. Introduction 2. Preliminaries 3. Main Results 4. Application to Integral Equations 5. Application to Homotopy References