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Abstract and Applied Analysis

Volume 2014 (2014), Article ID 803729, 11 pages

http://dx.doi.org/10.1155/2014/803729

## Tripled Coincidence and Common Fixed Point Results for Two Pairs of Hybrid Mappings

^{1}Department of Mathematics, King Abdul Aziz University, Jeddah, Saudi Arabia^{2}Department of Mathematics, COMSATS Institute of Information Technology, Chack Shahzad, Islamabad 44000, Pakistan^{3}Department of Mathematics & Applied Mathematics, University of Pretoria, Pretoria 002, South Africa^{4}Department of Mathematics, International Islamic University, H-10, Islamabad 44000, Pakistan

Received 26 August 2013; Accepted 24 December 2013; Published 30 January 2014

Academic Editor: Patricia J. Y. Wong

Copyright © 2014 Marwan Amin Kutbi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

The tripled fixed point is a generalization of the well-known concept of “coupled fixed point.” In this paper, tripled coincidence and common fixed point results for two hybrid pairs consisting of multivalued and single valued mappings on a metric space are proved. We give examples to illustrate our results. In the process, several comparable coincidence and fixed point results in the existing literature are improved, unified, and generalized.

#### 1. Introduction and Preliminaries

The study of fixed points for multivalued contraction mappings using the Hausdorff metric was initiated by Nadler Jr. [1]. After this, fixed point theory has been developed further and applied to many disciplines to solve functional equations. Banach contraction principle has been extended in different directions. Some authors used generalized contractions for multivalued mappings and hybrid pairs of single and multi-valued mappings, while others used more general spaces. Dhage [2, 3] established hybrid fixed point theorems and obtained some applications of presented results. Gnana Bhaskar and Lakshmikantham [4] introduced the notion of a coupled fixed point and proved some coupled fixed point results under certain contractive conditions in a complete metric space endowed with a partial order. They applied their results to study the existence and uniqueness of solution for a periodic boundary value problem associated with a first-order ordinary differential equation. Later, Lakshmikantham and Ciric [5] established the existence of coupled coincidence point results to generalize the results of Gnana Bhaskar and Lakshmikantham [4]; Karapinar [6] generalized these results on a complete cone metric space endowed with a partial order. Recently, Berinde and Borcut [7, 8] introduced the concept of a tripled fixed point for nonlinear contractive mappings in partially ordered complete metric spaces and obtained tripled coincidence and fixed point results for commuting maps. Hussain et al. [9, 10] obtained some coupled and tripled coincidence results without compatibility. Ilic et al. [11] obtained coupled coincidence and common fixed point theorems for a hybrid pair of mappings. For other related results in this direction, we refer to [12–16] and references mentioned therein. The purpose of this paper is to obtain tripled coincidence and common fixed point results for two hybrid pairs consisting of multivalued and single valued mappings.

Let us recall some definitions and well known results needed in the sequel.

Let be a metric space. For and , we denote . The set of all nonempty bounded and closed subsets of is denoted by . Let be the Hausdorff metric induced by the metric on ; that is, for every .

Lemma 1 (see [1]). *Let and . Then, for every , there exists such that
*

Lemma 2 (see [1]). *Let and . Then, for every , there exists such that
*

Lemma 3 (see [1]). *Let . If , then .*

*Definition 4. *Let be a nonempty set, (collection of all nonempty subsets of and . An element is called (i) a tripled fixed point of if , , and (ii) tripled coincidence point of a hybrid pair if , and (iii) tripled common fixed point of a hybrid pair if , , and .

We denote the set of tripled coincidence point of a hybrid pair by . Note that if , then and are also in .

*Definition 5. *Let and . Then the hybrid pair is called -compatible if whenever .

*Definition 6. *Let and . The mapping is called -idempotent at some point if , , and .

#### 2. Main Result

Theorem 7. *Let be a metric space, and let be mappings such that
**
for all , where , , are nonnegative real such that
**
If and is complete subset of , then and have tripled coincidence point. Moreover and have tripled common fixed point if one of the following conditions holds:**(i)** and are w-compatible, , and for some , and is continuous at , , ;**(ii)**if , , and and is -idempotent for ;**(iii)** is continuous at , , for some and for some ; ; and and .*

*Proof. *Let be arbitrary. Choose such that , and . Choose such that , , and . This can be done because . If
then
Imply that
As and are closed,
Similarly
Hence and are tripled coincidence points of pairs and , respectively. Now assume that , for some which gives that ; therefore, there exist
such that
Since , there exist , , , , , and in such that , , , , , and . Thus
Continuing this process, we obtain three sequences , , and in such that
with

By (4),
which further gives
Similarly it can be shown that
Again
which implies
Similarly, it can be shown that
Let
From (17) and (18), we get
From (20) and (21) we get
Adding (23) and (24), we obtain
Since by inequality (5), we get
Hence
Then from (27), we get
As ,
By the similar process as above, we can show that
Thus we have
Continuing this process, we obtain
Similarly
Continuation of this process implies that
By (32) and (34), we have
That is,
holds true for all , where
Now for every with , we have
Since , we conclude that , , and are Cauchy sequences in . By completeness of , there exists such that ,, and . Then from (4), we get
On taking limits as , we get
which implies that
And hence . Similarly , . And ,? , . Thus is a tripled coincidence point of and . Suppose that (i) holds; then, for some and , we have ,? , , and ,?? ,. Since and are -compatible, we have
for and . Since , and . So , , and . Similarly , , and . Continuing in this way, we get
which implies
for all and
Since and for and and is continuous at , and , so we have , , and . Now using (4), we get
On taking limits as , we get
which implies that
and hence
Similarly,
Consequently,
Similarly,
Hence is a tripled fixed point of and . Now suppose that (ii) holds. Since is , -idempotent for some and , we have , , , and , , . Since we have , and . So
Hence is a tripled common fixed point of and . Now suppose that (iii) holds. For some and , we get
Since is continuous at and , we get , , and . Thus
This implies that is a tripled common fixed point of and .

If in Theorem 7, ? ,? (the identity mapping), then we have the following result.

Corollary 8. *Let be a metric space and such that
**
for all , where , , are nonnegative real satisfy (5). Then has a fixed point.*

Corollary 9. *Let be a metric space and ??and?? be mappings such that
**
for all , where . If and is complete subset of . Then and have tripled coincidence point. Moreover and have tripled common fixed point if anyone of the conditions (i)–(iii) of Theorem 7 holds.*

Theorem 10. *Let be a metric space and and be mappings such that
**
for all , where . If and is complete subset of . Then and have tripled coincidence point. Moreover and have tripled common fixed point if one of the conditions (i)–(iii) of Theorem 7 holds.*

*Proof. *Let be arbitrary. Choose such that , and . Note that , and are well defined. Choose such that , , and . If , then following similar arguments to those given in Theorem 7, we obtain that and are tripled coincidence point and , respectively. Now assume that , set . Then , so there exists
such that
Since , there exist , , , , , and in such that , , , , , and . Thus
Continuing this process, we obtain sequences , , and in as , ? , , and , , such that

From (58), we have
Hence, if we suppose that , then
Therefore,
Similarly, we obtain