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# Some discussion on the existence of common fixed points for a pair of maps

- Deepesh K Patel
^{1}, - Poom Kumam
^{2}Email author and - Dhananjay Gopal
^{1}

**2013**:187

https://doi.org/10.1186/1687-1812-2013-187

© Patel et al.; licensee Springer 2013

**Received:**8 May 2013**Accepted:**26 June 2013**Published:**16 July 2013

## Abstract

In this paper, the concepts of conditionally sequential absorbing and pseudo-reciprocal continuous maps are introduced in connection to giving a brief discussion on the role of various types of commutativity (*e.g.*, weakly compatible, occasionally weakly compatible, subcompatible, pseudo-compatible, *etc.*) and continuity-type conditions (*e.g.*, reciprocal, weak reciprocal, *g*-reciprocal, conditionally reciprocal, subsequential and sequential continuity of type $({A}_{g})$ and $({A}_{f})$) in the context of existence of common fixed points of a pair of maps. Here, the utility of newly introduced maps (*i.e.*, conditionally sequential absorbing and pseudo-reciprocal continuous) in view of common fixed points for a pair of maps satisfying contractive as well as nonexpansive Lipschitz-type conditions is shown.

**MSC:**47H10, 54H25.

## Keywords

- common fixed point
- conditionally sequential absorbing
- pseudo-reciprocal continuity

## 1 Introduction and preliminaries

The classical results of Banach [1] (see also [2]) and Edelstein [3] have been the inspiration for many researchers working in the area of metric fixed point theory. In 1976, Jungck [4] generalized the Banach contraction principle by introducing the idea of commuting maps and settled the historical open problem that a pair of commuting and continuous self-mappings on the unit interval $[0,1]$ need not have a common fixed point [5, 6]. This result of Jungck [4] made foundation to study and investigate common fixed points and their applications in various other branches of mathematical sciences in the last five decades. Since then many fixed point theorists have attempted to find weaker forms of commutativity and continuity that may ensure the existence of a common fixed point for a pair of self-mappings on a metric space. Systematic observations and comparison of commutativity-type mappings are available in [7].

Proving a common fixed point for mappings satisfying Banach-type contractive conditions involves the following steps: step one is to show that there exists a Cauchy sequence which converges to a point in *X* (where *X* is complete); the second step is to show the existence of a coincidence point by assuming suitable weaker forms of commutativity and continuity conditions; and step three automatically gives rise to the fact that this coincidence point is a unique common fixed point due to the contractive condition. Observing carefully step two, one finds that showing the existence of a coincidence point for involved maps is nothing but assuming the existence of a coincidence point itself by a suitable choice of weaker forms of commutativity and continuity conditions (see, for instance, [8–16]).

Keeping the above facts in mind, Jungck and Rhoades [17] utilized the notion of occasionally weakly compatible maps introduced in [18] (as a generalization of weakly compatible maps) for those pairs which do have at least one coincidence point where the maps commute (it is well known that a pair of maps without a coincidence point is always vacuously weakly compatible) and obtained fixed point theorems for such maps.

On the other hand, Singh and Mishra in [19] illustrated a technique to prove the existence of a coincidence point without assuming continuity and commutativity-type conditions. Whereas the result of Suzuki and Pathak [20] does not involve any continuity-type conditions to prove the existence of a coincidence point as well as a common fixed point for a pair of maps (but they used weaker forms of commutativity conditions). It is also worth mentioning that Suzuki and Pathak [20] did not provide any illustrative examples to discuss and highlight the above facts. It is also important to note that none of the results of Jungck [9], Singh and Mishra [19] and Suzuki and Pathak [20] can be obtained from each other due to their different characteristics. These facts are illustrated in this paper via Example 2.6 (p.10).

Motivated by the works of Jungck and Rhoades [17], Bouhadjera and Thobie [21] (respectively Hussain *et al.* [22] and Sintunavarat and Kumam [23]) introduced the notion of subcompatible maps (respectively the notions of occasionally weakly $\mathcal{JH}$ operator and occasionally weakly biased maps) as generalization of occasionally weakly compatible maps and obtained fixed point theorems for such maps. However, Dorić *et al.* in [24] (respectively Alghamdi *et al.* [25]) showed that in the event of a pair of single-valued maps, the notion of occasionally weakly compatible (respectively occasionally weakly $\mathcal{JH}$ operator and occasionally weakly biased maps) reduces to weak compatibility due to the unique coincidence point of the involved maps, which is always ensured by underlying contractive conditions. Hence weak compatibility remains the minimal commutativity condition for the existence of a common fixed point for a contractive pair of maps. In view of these, the various results for occasionally weakly compatible maps (occasionally weakly $\mathcal{JH}$ operator and occasionally weakly biased maps) obtained in [17, 21, 22, 26–30], which were used under contractive conditions, do not yield real generalizations (see also [31, 32]). Considering these facts, Pant and Pant [33] (see also [34]) redefined the concept of occasionally weakly compatibility by introducing the idea of conditionally commuting maps which constitute a proper setting in the context of studying non-unique common fixed points for a pair of maps.

Possibly the first common fixed point theorem (respectively fixed point theorem) without any continuity requirement was established by Pant [12, 35] when he introduced the idea of noncompatible and reciprocal continuous maps. (However, the origin of metric fixed point theory for a single mapping without continuity requirement can be traced back to Kannan [36].) Recently, Pant *et al.* [37] and Pant and Bisht [38] generalized the notion of reciprocal continuity by introducing weak reciprocal continuity and conditionally reciprocal continuity and utilized the same to obtain some common fixed point theorems. In this connection, the recent paper of Gopal *et al.* [39] is also readable.

Motivated by the results of Pant and Bisht [38, 40], we introduce the concept of conditionally sequential absorbing and pseudo-reciprocal continuous maps, which allows us to give a comparative study of various types of commutativity conditions (*e.g.*, compatible, weakly compatible, occasionally weakly compatible, conditionally commuting, pseudo-compatible) and continuity-type conditions (*e.g.*, reciprocal, weak reciprocal, *g*-reciprocal, conditionally reciprocal, subsequential and sequential continuity of type $({A}_{g})$ and $({A}_{f})$) with these newly introduced notions in the context of existence of common fixed points of a pair of maps.

- (i)
compatible [9] iff ${lim}_{n}d(fg{x}_{n},gf{x}_{n})=0$ whenever $\{{x}_{n}\}$ is a sequence in

*X*such that ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some*t*in*X*.It is clear from the above definition that

*f*and*g*will be noncompatible [35] if there exists a sequence $\{{x}_{n}\}$ in*X*such that ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some*t*in*X*, but ${lim}_{n}d(fg{x}_{n},gf{x}_{n})$ is either nonzero or non-existent; - (ii)
*f*-compatible [41] if ${lim}_{n}d(fg{x}_{n},gg{x}_{n})=0$ whenever $\{{x}_{n}\}$ is a sequence in*X*such that ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some*t*in*X*; - (iii)
*g*-compatible [41] if ${lim}_{n}(ff{x}_{n},gf{x}_{n})=0$ whenever $\{{x}_{n}\}$ is a sequence in*X*such that ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some*t*in*X*; - (iv)
weakly compatible [42] if the mappings commute at their coincidence points,

*i.e.*, $fx=gx$ for some $x\in X$ implies $fgx=gfx$; - (v)
occasionally weakly compatible [17] if there exists a point

*x*in*X*that is a coincidence point of*f*and*g*at which*f*and*g*commute; - (vi)
subcompatible [21] iff there exists a sequence $\{{x}_{n}\}$ in

*X*such that ${lim}_{n}d(fg{x}_{n},gf{x}_{n})=0$ with ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some $t\in X$; - (vii)
conditionally commuting [33] if they commute on a nonempty subset of the set of coincidence points whenever the set of their coincidence point is nonempty;

- (viii)
conditionally compatible [34] iff, whenever the set of sequences $\{{x}_{n}\}$ satisfying ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}$ is nonempty, there exists a sequence $\{{y}_{n}\}$ such that ${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=t$ (say) and ${lim}_{n}d(fg{y}_{n},gf{y}_{n})=0$;

- (ix)
pseudo-compatible [40] iff, whenever the set of sequences $\{{x}_{n}\}$ satisfying ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}$ is nonempty, there exists a sequence $\{{y}_{n}\}$ such that ${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=t$ (say), ${lim}_{n}d(fg{y}_{n},gf{y}_{n})=0$; and ${lim}_{n}d(fg{z}_{n},gf{z}_{n})=0$ for any associated sequence $\{{z}_{n}\}$ of $\{{y}_{n}\}$.

- (i)
reciprocally continuous [12, 43] iff ${lim}_{n}fg{x}_{n}=ft$ and ${lim}_{n}gf{x}_{n}=gt$ whenever $\{{x}_{n}\}$ is a sequence in

*X*such that ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some*t*in*X*; - (ii)
weakly reciprocally continuous [37] if ${lim}_{n}fg{x}_{n}=ft$ or ${lim}_{n}gf{x}_{n}=gt$ whenever $\{{x}_{n}\}$ is a sequence in

*X*such that ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some*t*in*X*; - (iii)
conditionally reciprocally continuous (CRC) [38] if, whenever the set of sequences $\{{x}_{n}\}$ satisfying ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}$ is nonempty, there exists a sequence $\{{y}_{n}\}$ satisfying ${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=t$ (say) such that ${lim}_{n}fg{y}_{n}=ft$ and ${lim}_{n}gf{y}_{n}=gt$;

- (iv)
*g*-reciprocally continuous [40] iff ${lim}_{n}ff{x}_{n}=ft$ and ${lim}_{n}gf{x}_{n}=gt$ whenever $\{{x}_{n}\}$ is a sequence such that ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some*t*in*X*; - (v)
sequentially continuous of type $({A}_{g})$ [39] iff there exists a sequence $\{{x}_{n}\}$ in

*X*such that ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some $t\in X$ satisfying ${lim}_{n}ff{x}_{n}=ft$ and ${lim}_{n}gf{x}_{n}=gt$; - (vi)
sequentially continuous of type $({A}_{f})$ [39] iff there exists a sequence $\{{x}_{n}\}$ in

*X*such that ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some $t\in X$ satisfying ${lim}_{n}fg{x}_{n}=ft$ and ${lim}_{n}gg{x}_{n}=gt$; - (vii)
subsequentially continuous [21] iff there exists a sequence ${x}_{n}$ in

*X*such that ${lim}_{n}fg{x}_{n}=ft$ and ${lim}_{n}gf{x}_{n}=gt$ with ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some $t\in X$.

**Theorem 1.1** [40]

*Let*

*f*

*and*

*g*

*be*

*g*-

*reciprocally continuous self*-

*mappings of a complete metric space*$(X,d)$

*such that*

- (i)
$fX\subseteq gX$;

- (ii)
$d(fx,fy)\le kd(gx,gy)$, $k\in [0,1)$.

*If* *f* *and* *g* *are pseudo*-*compatible*, *then* *f* *and* *g* *have a unique common fixed point*.

**Theorem 1.2** [40]

*Let*

*f*

*and*

*g*

*be*

*g*-

*reciprocally continuous noncompatible self*-

*mappings of a metric space*$(X,d)$

*such that*

- (i)
$fX\subseteq gX$;

- (ii)
$d(fx,fy)<max\{d(gx,gy),\frac{k[d(fx,gx)+d(fy,gy)]}{2},\frac{d(fx,gy)+d(fy,gx)}{2}\}$,

*where*$1\le k<2$; - (iii)
$d(x,fx)\ne max\{d(x,gx),d(fx,gx)\}$,

*whenever the right*-*hand side is nonzero*. *If* *f* *and* *g* *are pseudo*-*compatible*, *then* *f* *and* *g* *have a unique common fixed point*.

**Theorem 1.3** [34]

*Let*

*f*

*and*

*g*

*be conditionally compatible self*-

*mappings of a metric space*$(X,d)$

*satisfying*

*whenever the right*-*hand side is nonzero*. *If* *f* *and* *g* *are noncompatible and reciprocally continuous*, *then* *f* *and* *g* *have a common fixed point*.

**Theorem 1.4** [38]

*Let*

*f*

*and*

*g*

*be conditionally reciprocal continuous self*-

*mappings of a complete metric space*$(X,d)$

*such that*

- (i)
$fX\subseteq gX$;

- (ii)
$d(fx,fy)\le kd(gx,gy)$, $k\in [0,1)$.

*If* *f* *and* *g* *are either compatible or* *g*-*compatible or* *f*-*compatible*, *then* *f* *and* *g* *have a unique common fixed point*.

**Theorem 1.5** [44]

*Let*$(X,d)$

*be a complete metric space*,

*let*

*f*

*and*

*g*

*be two noncompatible self*-

*mappings on*

*X*

*satisfying*

*where*$\phi :[0,\mathrm{\infty})\to [0,\mathrm{\infty})$

*is a continuous from right and nondecreasing function such that*$\phi (t)<t$

*for all*$t>0$.

*Assume that*

- (i)
$\overline{f(X)}\subseteq g(X)$,

- (ii)
$max\{d(ggx,fgx),d(ffx,gfx)\}\le \phi (d(fx,gx))$

*for all*$x\in X$*and* - (iii)
$\phi (d(fx,{f}^{2}x))\ne \phi (max\{d(gx,gfx),d({g}^{2}x,gfx),d(fx,gx),d({f}^{2}x,gfx),d(fx,gfx),d(gx,{f}^{2}x)\})$,

*whenever*$fx\ne {f}^{2}x$.

*Then* *f* *and* *g* *have a unique common fixed point*. *Also*, *f* *and* *g* *are discontinuous at the common fixed point*.

## 2 Main results

We begin with the following example.

**Example 2.1**Let $X=[2,20]$ and

*d*be the usual metric on

*X*. Define self-mappings

*f*and

*g*on

*X*as follows:

Then we can see that $f(X)=(4,5]\subseteq (4,6]\cup \{20\}=g(X)$ and the pair $(f,g)$ is *g*-reciprocally continuous. It can be verified that $d(fx,fy)\le kd(gx,gy)$ for all $x,y\in X$ with $k=\frac{1}{2}$. Thus, *f* and *g* satisfy all the conditions of Theorem 1.1 except pseudo-compatibility. For the pseudo-compatibility, consider the only existent sequence ${x}_{n}={y}_{n}=2+\frac{1}{n}$, then we have ${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=4$, but ${lim}_{n}fg{y}_{n}={lim}_{n}f(4+\frac{2}{n})=5$, ${lim}_{n}gf{y}_{n}={lim}_{n}(4+\frac{1}{n})=20$, and so ${lim}_{n}d(fg{y}_{n},gf{y}_{n})=15\ne 0$. Also note that the pair $(f,g)$ is not compatible. Here, $(f,g)$ has no coincidence point therefore it is also not an occasionally weakly compatible but vacuously weakly compatible pair.

This suggests that pseudo-compatible is stronger than weakly compatible (and occasionally weakly compatible) in the context of Theorem 1.1 (such an observation is missing in [40]).

The above example motivated us to define the following.

**Definition 2.1** Two self-mappings *f* and *g* of a metric space $(X,d)$ are called conditionally sequential absorbing if, whenever the set of sequences $\{{x}_{n}\}$ satisfying ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}$ is nonempty, there exists a sequence $\{{y}_{n}\}$ satisfying ${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=t$ (say) such that ${lim}_{n}d(f{y}_{n},fg{y}_{n})=0$ and ${lim}_{n}d(g{y}_{n},gf{y}_{n})=0$.

**Example 2.2**Let $X=[2,10]$ and let

*d*be the usual metric on

*X*. Define $f,g:X\to X$ as follows:

Then the maps are conditionally sequential absorbing. To view this, consider the constant sequence ${x}_{n}=2$. However, the pair $(f,g)$ is not weakly compatible as they do not commute at their coincidence point $x=3$. It may be noted that $x=2$ and $x=3$ are two coincidence points of *f* and *g*. But in respect of the unique coincidence point (common fixed point), conditionally sequential absorbing always implies weakly compatible and hence occasionally weakly compatible and pseudo-compatible, because the maps naturally commute at their unique coincidence point (common fixed point).

**Example 2.3**Let $X=[0,1]$ and let

*d*be the usual metric on

*X*. Define $f,g:X\to X$ as follows:

Then *f* and *g* are weakly compatible but not conditionally sequential absorbing. Here, $x=0$ and $x=1$ are two coincidence points.

**Remark 2.1** In Example 2.1, the pair $(f,g)$ is vacuously weakly compatible but not conditionally sequential absorbing and not pseudo-compatible. Note that *f* and *g* do not have any coincidence point. In Example 2.2, the pair $(f,g)$ is conditionally sequential absorbing but not weakly compatible. In Example 2.3, the pair $(f,g)$ is weakly compatible but not conditionally sequential absorbing.

Thus, as definitions, weakly compatible, pseudo-compatible and conditionally sequential absorbing are very different. However, in the context of a unique coincidence point, conditionally sequential absorbing is stronger than weakly compatible, which will be shown in our Example 2.6.

**Example 2.4**Let $X=[0,+\mathrm{\infty})$ and let

*d*be the usual metric on

*X*. Define $f,g:X\to X$ as follows:

*f*and

*g*are conditionally reciprocal continuous and subsequentially continuous. We can see that

*f*and

*g*are neither weak reciprocal continuous nor

*g*-reciprocal continuous. To see this, consider the sequence ${x}_{n}=1+\frac{1}{n}$ for $n=1,2,\dots $ , then

Note that *f* and *g* do not have a coincidence point.

**Example 2.5**Let $X=R$ and let

*d*be the usual metric on

*X*. Define $f,g:X\to X$ as follows:

Then it is easy to see that the pair $(f,g)$ is reciprocal continuous, weak reciprocally continuous and conditionally reciprocally continuous but neither subsequentially continuous nor sequentially continuous of type $({A}_{g})$ and $({A}_{f})$. Note that the pair has no coincidence point.

In view of the above examples, we observe that in the event of no coincidence point, subsequential continuity as well as sequential continuity of type $({A}_{g})$ and $({A}_{f})$ are different from reciprocal continuity (respectively *g*-reciprocal and conditionally reciprocal continuity). However, in the context of a unique coincidence point (common fixed point), subsequential continuity as well as sequential continuity of type $({A}_{g})$ and $({A}_{f})$ are equivalent to conditionally reciprocal continuity.

The motivation of the following definition can be predicted from the proof of the last step in our Theorem 2.1.

**Definition 2.2** Two self-mappings *f* and *g* of a metric space $(X,d)$ are called pseudo-reciprocal continuous (PRC) (with respect to conditionally sequential absorbing) if, whenever the set of sequences $\{{x}_{n}\}$ satisfying ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}$ is nonempty, there exists a sequence $\{{y}_{n}\}$ (satisfying ${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=t$ (say), ${lim}_{n}d(f{y}_{n},fg{y}_{n})=0$ and ${lim}_{n}d(g{y}_{n},gf{y}_{n})=0$) such that ${lim}_{n}fg{y}_{n}=ft$ and ${lim}_{n}gf{y}_{n}=gt$.

### Common fixed point theorems

- (a)
*ϕ*is nondecreasing, continuous and $\varphi (0)=0<\varphi (t)$ for every $t>0$; - (b)
*ψ*is nondecreasing, right-continuous, and $\psi (t)<t$ for every $t>0$.

To prove our first result, we use the following lemma.

**Lemma 2.1** [45]

*For every function*$\psi :[0,\mathrm{\infty})\to [0,\mathrm{\infty})$,

*let*${\psi}^{n}$

*be the*$nth$

*iterate of*

*ψ*.

*Then the following hold*:

- (i)
*if**ψ**is nondecreasing*,*then for each*$t>0$, ${lim}_{n\to \mathrm{\infty}}{\psi}^{n}(t)=0$*implies*$\psi (t)<t$; - (ii)
*if**ψ**is right*-*continuous with*$\psi (t)<t$*for*$t>0$,*then*${lim}_{n\to \mathrm{\infty}}{\psi}^{n}(t)=0$.

**Theorem 2.1**

*Let*

*f*

*and*

*g*

*be two pseudo*-

*reciprocal continuous*(

*w*.

*r*.

*t*.

*conditionally sequential absorbing*)

*self*-

*mappings of a complete metric space*$(X,d)$

*such that*$fX\subseteq gX$,

*and let*$\varphi ,\psi :[0,\mathrm{\infty})\to [0,\mathrm{\infty})$

*be two functions satisfying*(a)

*and*(b).

*If for all*$x,y\in X$,

*where*

*then* *f* *and* *g* *have a unique common fixed point provided* $(f,g)$ *is conditionally sequential absorbing*.

*Proof*Let ${x}_{0}\in X$ and since $fX\subseteq gX$, so we have a sequence $\{{p}_{n}\}$ defined by

*n*we have either ${p}_{n}={p}_{n-1}$ or ${p}_{n}={p}_{n+1}$, then by condition (2.1) we obtain that the sequence $\{{p}_{n}\}$ is definitely constant and thus it is a Cauchy sequence. Suppose ${p}_{n}\ne {p}_{n-1}$ for each

*n*, then from condition (2.1) we have

Now we prove that $\{{p}_{n}\}$ is Cauchy.

*m*and

*n*with $m<n$. This assumes that there exist two sequences $\{{m}_{k}\}$, $\{{n}_{k}\}$ of natural numbers with ${m}_{k}<{n}_{k}$ such that

*k*. Then from

*ϕ*being continuous and

*ψ*right-continuous, we get

*X*such that $f{y}_{n}\to u$, $g{y}_{n}\to u$ (say) satisfying

In view of (2.11) and (2.12), we get $fu=gu=u$, *i.e.*, *u* is a common fixed point of *f* and *g*. The uniqueness of a common fixed point follows easily from contractive condition (2.1). □

**Example 2.6**Let $X=[0,1]$ with the usual metric

*d*. Define self-maps

*f*and

*g*as follows:

*f*and

*g*satisfy all the conditions of Theorem 2.1 with $f(X)=[\frac{1}{2},\frac{3}{4})\subseteq [\frac{1}{2},1)=g(X)$. Here,

*f*and

*g*are conditionally sequential absorbing and pseudo-reciprocal continuous (w.r.t. conditionally sequential absorbing) in respect of the constant sequence ${x}_{n}=\frac{1}{2}$. Let us consider the sequence ${x}_{n}=\frac{1}{n+2}$, then

Thus, $(f,g)$ is not a reciprocal as well as not a *g*-reciprocal continuous pair. Also the pair $(f,g)$ is neither compatible, *f*-compatible nor *g*-compatible.

If we take $\varphi (t)=t$ and $\psi (t)=kt$, $k\in [0,1)$, then it can be verified that *f* and *g* satisfy contraction condition (2.1) with $k=\frac{5}{6}$. Here, $x=\frac{1}{2}$ is the unique common fixed point of *f* and *g*, which is also a point of discontinuity.

*f*and

*g*do not satisfy the condition

used in Theorem 1.5. Here, it is worth noting that none of the earlier relevant theorems, for example, Theorem 1.1, Theorem 1.4 and Theorem 1.5, can be used in the context of this example. One more interesting part of this example is that neither $f(X)$ nor $g(X)$ is closed. Thus the result of Singh and Mishra [19] cannot be applicable in the context of this example.

**Theorem 2.2**

*Let*

*f*

*and*

*g*

*be pseudo*-

*reciprocal continuous*(

*w*.

*r*.

*t*.

*conditionally sequential absorbing*)

*and noncompatible self*-

*mappings of a metric space*$(X,d)$

*satisfying*

*where* $1\le k<2$. *If* *f* *and* *g* *are conditionally sequential absorbing*, *then* *f* *and* *g* *have a unique common fixed point*.

*Proof* Since *f* and *g* are noncompatible maps, there exists a sequence $\{{x}_{n}\}$ in *X* such that $f{x}_{n}\to t$ and $g{x}_{n}\to t$ for some *t* in *X* but either ${lim}_{n}d(fg{x}_{n},gf{x}_{n})\ne 0$ or the limit does not exist. Also, the pair $(f,g)$ is conditionally sequential absorbing; therefore, there exists a sequence $\{{y}_{n}\}$ in *X* such that ${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=u$ (say) with ${lim}_{n}d(f{y}_{n},fg{y}_{n})=0$ and ${lim}_{n}d(g{y}_{n},gf{y}_{n})=0$. Now, by the pseudo-reciprocal continuity (w.r.t. conditionally sequential absorbing) of the pair $(f,g)$, we have $fg{y}_{n}\to fu$ and $gf{y}_{n}\to gu$. In view of these limits, we get *u* is a common fixed point of *f* and *g*.

*w*of

*f*and

*g*such that $w\ne u$. Then, on using (2.13), we have

Thus, we have $d(w,u)<\frac{k}{2}d(w,u)<d(w,u)$, a contradiction and hence $w=u$. □

**Example 2.7**Again consider Example 2.6 wherein the pair $(f,g)$ satisfies all the conditions of Theorem 2.2 for all $k\in [1,2)$. Note that at $x=0$,

*f*and

*g*do not satisfy the condition

whenever the right-hand side is nonzero. Thus Theorem 2.2 is a genuine extension and improvement of Theorem 1.2 due to Pant and Bisht [40].

**Observation** The proof of Theorem 2.1, Theorem 2.2 and examples above immediately suggest us defining another type of continuity as follows.

**Definition 2.3** Two self-mappings *f* and *g* of a metric space $(X,d)$ are called pseudo-reciprocal continuous (PRC) (with respect to pseudo-compatible) if whenever the set of sequences $\{{x}_{n}\}$ satisfying ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}$ is nonempty, there exists a sequence $\{{y}_{n}\}$ (satisfying ${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=t$ (say); ${lim}_{n}d(fg{y}_{n},gf{y}_{n})=0$; and ${lim}_{n}d(fg{z}_{n},gf{z}_{n})=0$ for any associated sequence $\{{z}_{n}\}$ of $\{{y}_{n}\}$) such that ${lim}_{n}fg{y}_{n}=ft$ and ${lim}_{n}gf{y}_{n}=gt$.

However, the notions of pseudo-compatibility and pseudo-reciprocal continuity (w.r.t. pseudo-compatibility) are no more applicable in the context of the existence of non-unique common fixed points for a pair of maps. This fact is illustrated in Example 2.11 below. At the same time, conditionally sequential absorbing and pseudo-reciprocal continuity (w.r.t. conditionally sequential absorbing) are easily applicable.

**Theorem 2.3** *Let* *f* *and* *g* *be reciprocal* (*or* *g*-*reciprocal*) *continuous and noncompatible self*-*mappings of a metric space* $(X,d)$ *satisfying* (2.13). *Then the pair* $(f,g)$ *has a unique common fixed point provided it is conditionally sequential absorbing*. *Moreover*, *f* *and* *g* *are discontinuous at the common fixed point*.

*Proof* Since *f* and *g* are noncompatible, there exists a sequence $\{{x}_{n}\}$ in *X* such that ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some $t\in X$, but ${lim}_{n}d(fg{x}_{n},gf{x}_{n})$ is either nonzero or not existent. Also, since *f* and *g* are conditionally sequential absorbing and ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$, there exists a sequence $\{{y}_{n}\}$ in *X*, satisfying ${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=u$ (say), such that ${lim}_{n}d(f{y}_{n},fg{y}_{n})=0$ and ${lim}_{n}d(g{y}_{n},gf{y}_{n})=0$. The reciprocal continuity of the pair $(f,g)$ implies that ${lim}_{n}fg{y}_{n}=fu$ and ${lim}_{n}gf{y}_{n}=gu$. Thus, in view of these limits, we obtain $fu=gu=u$. If we consider the pair $(f,g)$ *g*-reciprocal continuous, then we have ${lim}_{n}ff{y}_{n}=fu$ and ${lim}_{n}gf{y}_{n}=gu$. Since ${lim}_{n}d(g{y}_{n},gf{y}_{n})=0$, so we have $gu=u$. Now, suppose $fu\ne u$. On using (2.13), we get $d(fu,u)<\frac{k}{2}d(fu,u)<d(fu,u)$, a contradiction and hence $fu=u$. Thus *u* is a common fixed point of *f* and *g*. Applying (2.13), we can show the uniqueness of the common fixed point.

We now show that *f* and *g* are discontinuous at the common fixed point *u*. If possible, suppose *f* is continuous at *u*. Then, considering the sequence $\{{x}_{n}\}$ of the present theorem and on using (2.13), we get $t=u$ and hence by the continuity of *f*, we have $ff{x}_{n}\to fu=u$ and $fg{x}_{n}\to fu=u$. Now, reciprocal (or *g*-reciprocal) continuity of the pair $(f,g)$ implies that $gf{x}_{n}\to gu=u$. This further yields that ${lim}_{n}d(fg{x}_{n},gf{x}_{n})=0$, which contradicts the fact that ${lim}_{n}d(fg{x}_{n},gf{x}_{n})$ is either nonzero or non-existent. Hence *f* is discontinuous at the fixed point.

Next, suppose that *g* is continuous at *u*. Then, for the sequence $\{{x}_{n}\}$, we get $gf{x}_{n}\to gu=u$ and $gg{x}_{n}\to gu=u$. If $(f,g)$ is reciprocal continuous, then we have $fg{x}_{n}\to fu=u$, and if it is *g*-reciprocal continuous, then on using (2.13), we get $fg{x}_{n}\to fu=u$. Thus, we obtain ${lim}_{n}d(fg{x}_{n},gf{x}_{n})=0$, a contradiction. Therefore *f* and *g* are discontinuous at their common fixed point. □

**Example 2.8**Let $X=[2,20]$ with the usual metric

*d*. Define $f,g:X\to X$ as follows:

Then *f* and *g* satisfy all the conditions of Theorem 2.3. It can be verified in this example that *f* and *g* satisfy contractive condition (2.13) for all $k\in [1,2)$. To see that *f* and *g* are noncompatible, consider the sequence $\{{x}_{n}\}$ in *X* such that ${x}_{n}=5+{\u03f5}_{n}$, then $f{x}_{n}\to 2$, $g{x}_{n}=(2+\frac{{\u03f5}_{n}}{3})\to 2$, $fg{x}_{n}\to 4$, $gf{x}_{n}\to 2$, and so ${lim}_{n}d(fg{x}_{n},gf{x}_{n})\ne 0$. Also here the pair $(f,g)$ is *g*-reciprocal continuous. To see this, let $\{{x}_{n}\}$ be a sequence in *X* such that ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}=t$ for some *t* in *X*. Then $t=2$, ${x}_{n}=2$ or ${x}_{n}=5+{\u03f5}_{n}$, $ff{x}_{n}\to 2=f(2)$ and $gf{x}_{n}\to 2=g(2)$. The pair $(f,g)$ is conditionally sequential absorbing in respect of the constant sequence $\{{y}_{n}\}$ given by ${y}_{n}=2$. Here, $x=2$ is the unique common fixed point where *f* and *g* are discontinuous.

*f*and

*g*do not satisfy the condition

*f*and

*g*do not satisfy

Thus, Theorem 2.3 is a genuine extension and improvement of Theorem 1.2 due to Pant and Bisht [40] and Theorem 1.5 due to Rezapour and Shahzad [44].

In the absence of contractive condition (2.13), the following corollaries are straightforward from Theorems 2.2 and 2.3.

**Corollary 2.1** *Let* *f* *and* *g* *be pseudo*-*reciprocal continuous* (*w*.*r*.*t*. *conditionally sequential absorbing*) *and noncompatible self*-*mappings of a metric space* $(X,d)$. *Then* *f* *and* *g* *have a common fixed point provided it is conditionally sequential absorbing*.

**Corollary 2.2** *Let* *f* *and* *g* *be reciprocal* (*or* *g*-*reciprocal*) *continuous and noncompatible self*-*mappings of a metric space* $(X,d)$. *Then the pair* $(f,g)$ *has a common fixed point provided it is conditionally sequential absorbing*.

The following examples illustrate the above corollaries.

**Example 2.9**Consider $X=[2,23]$ and let

*d*be the usual metric on

*X*. Define $f,g:X\to X$ as

*f*and

*g*satisfy all the conditions of Corollary 2.1. In view of the constant sequence ${x}_{n}=2$ or ${x}_{n}=11$, the pair $(f,g)$ is conditionally sequential absorbing and pseudo-reciprocal continuous (w.r.t. conditionally sequential absorbing). For noncompatibility as well as non-reciprocal continuity, let us consider the sequence ${x}_{n}=5+(\frac{1}{n})$, then we have

and so ${lim}_{n}d(fg{x}_{n},gf{x}_{n})\ne 0$. Here, 2 and 11 are two common fixed points of *f* and *g*. Also the pair is not weakly compatible as *f* and *g* do not commute at their coincidence point $x=23$.

- (i)
$d(x,fx)\ne max\{d(x,gx),d(fx,gx)\}$,

- (ii)
$d(x,gx)\ne max\{d(x,gx),d(gx,fx)\}$,

- (iii)
$d(x,gx)\ne max\{d(x,fx),d(gx,fx)\}$, and

- (iv)
$d(fx,{f}^{2}x)\ne max\{d(gx,gfx),d(fx,gx),d({f}^{2}x,gfx),d(fx,gfx),d(gx,{f}^{2}x)\}$,

whenever the right-hand side is nonzero. Here, it is worth noting that none of the Theorem 1.3 due to Pant and Bisht [34] and the main results contained in Pant and Pant [33] and Gopal *et al.* [46] can be used in the context of Corollary 2.1.

**Example 2.10**Consider $X=[2,23]$ and let

*d*be the usual metric on

*X*. Define $f,g:X\to X$ as

therefore ${lim}_{n}d(fg{x}_{n},gf{x}_{n})\ne 0$, and so $(f,g)$ is noncompatible. Here, 2 and 11 are two common fixed points of *f* and *g*.

Finally, we present an example which shows that the requirement of conditionally sequential absorbing property is necessary for producing common fixed points of mappings satisfying non-expansive or Lipschitz-type conditions besides exhibiting the limitations of commuting properties of the pairs utilized in earlier related results of Pant and Bisht [34], Pant and Pant [33] and Jungck and Rhoades [17].

**Example 2.11**Let $X=[2,20]$ endowed with the usual metric

*d*and $f,g:X\to X$ by

Then by a routine calculation, it can be verified that $\overline{f(X)}\subseteq g(X)$ and $d(fx,fy)\le kd(gx,gy)$ for all $x,y\in X$, where $k\ge 0$. Also, *f* and *g* are a noncompatible and weakly commuting (and hence occasionally weakly compatible and conditionally commuting) pair. In order to show that $(f,g)$ is noncompatible, the sequence ${x}_{n}=5+1/n$; $n>1$, $n\in N$ satisfies the requirements. Also, it is straightforward to verify that the pair $(f,g)$ is pseudo-compatible as well as pseudo-reciprocal continuous (w.r.t. pseudo-compatible), but the pair is not conditionally sequential absorbing in respect of ${x}_{n}=6$ or $5+1/n$. On the other hand, at $x=6$, it can be verified that the mappings *f* and *g* do not satisfy any one of the conditions described by (i), (ii), (iii) or (iv) mentioned earlier. Notice that the estimated pair has no common fixed point.

**Observations**The following definitions can be considered as variants of conditionally sequential absorbing. Two self-mappings

*f*and

*g*of a metric space $(X,d)$ are called conditionally sequential absorbing

- (i)
*of type*(A)*if, whenever the set of sequences*$\{{x}_{n}\}$*satisfying*${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}$*is nonempty, there exists a sequence*$\{{y}_{n}\}$*satisfying*${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=t$*(say) such that*${lim}_{n}d(f{y}_{n},ff{y}_{n})=0$*and*${lim}_{n}d(g{y}_{n},gf{y}_{n})=0$*;* - (ii)
*of type*(B)*if, whenever the set of sequences*$\{{x}_{n}\}$*satisfying*${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}$*is nonempty, there exists a sequence*$\{{y}_{n}\}$*satisfying*${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=t$*(say) such that*${lim}_{n}d(f{y}_{n},fg{y}_{n})=0$*and*${lim}_{n}d(g{y}_{n},gg{y}_{n})=0$*;* - (iii)
*of type*(C)*if, whenever the set of sequences*$\{{x}_{n}\}$*satisfying*${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}$*is nonempty, there exists a sequence*$\{{y}_{n}\}$*satisfying*${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=t$*(say) such that*${lim}_{n}d(f{y}_{n},ff{y}_{n})=0$*and*${lim}_{n}d(g{y}_{n},gg{y}_{n})=0$*.*

We can have some more variants by interchanging the place of *f* and *g*. In respect of these variants, we can also define the corresponding pseudo-reciprocal continuity, for example, *two self-mappings* *f* *and* *g* *of a metric space* $(X,d)$ *are called pseudo-reciprocal continuous of type (A) if, whenever the set of sequences* $\{{x}_{n}\}$ *satisfying* ${lim}_{n}f{x}_{n}={lim}_{n}g{x}_{n}$ *is nonempty, there exists a sequence* $\{{y}_{n}\}$ (*satisfying* ${lim}_{n}f{y}_{n}={lim}_{n}g{y}_{n}=t$ *(say),* ${lim}_{n}d(f{y}_{n},ff{y}_{n})=0$ *and* ${lim}_{n}d(g{y}_{n},gf{y}_{n})=0$) *such that* ${lim}_{n}ff{y}_{n}=ft$ *and* ${lim}_{n}gf{y}_{n}=gt$*.*

**Remark 2.2** The conclusion of our previous results will remain true if we replace the conditionally sequential absorbing and pseudo-reciprocal continuity by any one of the above variants of conditionally sequential absorbing and corresponding pseudo-reciprocal continuity. However, in the context of a unique coincidence or common fixed point, all these variants coincide with each others.

## Declarations

### Acknowledgements

The second author thanks for the support of the King Mongkut’s University of Technology Thonburi (KMUTT) and the third author is supported by CSIR, Govt. of India, grant number 25(0215)/13/EMR-II.

## Authors’ Affiliations

## References

- Banach S: Sur les operations dans les ensembles abstraits et leur applications aux equations intégrales.
*Fundam. Math.*1922, 3: 133-181.Google Scholar - Caccioppoli R: Un teorema generale sull’esistenza di elementi uniti in una trasformazione funzionale.
*Rend. Lincei Mat. Appl.*1930, 11: 794-799. (in Italian)Google Scholar - Edelstein M: On fixed points and periodic points under contractive mappings.
*J. Lond. Math. Soc.*1962, 1: 74-79.MathSciNetView ArticleGoogle Scholar - Jungck G: Commuting mappings and fixed points.
*Am. Math. Mon.*1976, 73: 261-263.MathSciNetView ArticleGoogle Scholar - Boyce WM: Commuting functions with no common fixed point.
*Trans. Am. Math. Soc.*1969, 137: 77-92.MathSciNetView ArticleGoogle Scholar - Huneke JP: On common fixed points of commuting continuous functions on an interval.
*Trans. Am. Math. Soc.*1969, 139: 371-381.MathSciNetView ArticleGoogle Scholar - Murthy PP: Important tools and possible applications of metric fixed point theory.
*Nonlinear Anal.*2001, 47: 3479-3490. 10.1016/S0362-546X(01)00465-5MathSciNetView ArticleGoogle Scholar - Chauhan S, Sintunavarat W, Kumam P: Common fixed point theorems for weakly compatible mappings in fuzzy metric spaces using (JCLR) property.
*Appl. Math.*2012, 3(9):976-982. 10.4236/am.2012.39145View ArticleGoogle Scholar - Jungck G: Compatible mappings and common fixed points.
*Int. J. Math. Math. Sci.*1986, 9(4):771-779. 10.1155/S0161171286000935MathSciNetView ArticleGoogle Scholar - Karapinar E, Patel DK, Imdad M, Gopal D:Some nonunique common fixed point theorems in symmetric spaces through $CL{R}_{(S,T)}$ property.
*Int. J. Math. Math. Sci.*2013., 2013: Article ID 753965Google Scholar - Pant RP: Common fixed points of noncommuting mappings.
*J. Math. Anal. Appl.*1994, 188: 436-440. 10.1006/jmaa.1994.1437MathSciNetView ArticleGoogle Scholar - Pant RP: Common fixed points of four mappings.
*Bull. Calcutta Math. Soc.*1998, 90: 281-286.MathSciNetGoogle Scholar - Pathak HK, Cho YJ, Kang SM: Remarks on
*R*-weakly commuting mappings and common fixed point theorems.*Bull. Korean Math. Soc.*1997, 34(2):247-257.MathSciNetGoogle Scholar - Sessa S: On a weak commutative condition of maps in fixed point consideration.
*Publ. Inst. Math. (Belgr.)*1982, 32(46):149-153.MathSciNetGoogle Scholar - Sintunavarat W, Kumam P: Common fixed point theorems for a pair of weakly compatible mappings in fuzzy metric spaces.
*J. Appl. Math.*2011., 2011: Article ID 637958Google Scholar - Sintunavarat W, Kumam P: Common fixed points for
*R*-weakly commuting in fuzzy metric spaces.*Ann. Univ. Ferrara*2012, 58: 389-406. 10.1007/s11565-012-0150-zMathSciNetView ArticleGoogle Scholar - Jungck G, Rhoades BE: Fixed point theorems for occasionally weakly compatible mappings.
*Fixed Point Theory*2006, 7(2):287-296. (Erratum: Fixed Point Theory 9, 383-384 (2008))MathSciNetGoogle Scholar - Al-Thagafi MA, Shahzad N: Generalized
*I*-nonexpansive selfmaps and invariant approximations.*Acta Math. Sin.*2008, 24: 867-876. 10.1007/s10114-007-5598-xMathSciNetView ArticleGoogle Scholar - Singh SL, Mishra SN: Remarks on Jachymski’s fixed point theorems for compatible maps.
*Indian J. Pure Appl. Math.*1997, 28: 611-645.MathSciNetGoogle Scholar - Suzuki T, Pathak HK: Almost biased mappings and almost compatible mappings are equivalent under some condition.
*J. Math. Anal. Appl.*2010, 368: 211-217. 10.1016/j.jmaa.2010.02.003MathSciNetView ArticleGoogle Scholar *Bouhadjera, H, Godet-Thobie, C: Common fixed point theorems for pair of subcompatible maps. arXiv:0906.3159v2 [math.FA]*. e-printatarXiv.org- Hussain N, Khamsi MA, Latif A: Common fixed points for JH-operators and occasionally weakly biased pairs under relaxed conditions.
*Nonlinear Anal.*2011, 74: 2133-2140. 10.1016/j.na.2010.11.019MathSciNetView ArticleGoogle Scholar - Sintunavarat W, Kumam P:Common fixed point theorems for generalized $\mathcal{JH}$-operator classes and invariant approximations.
*J. Inequal. Appl.*2011., 2011: Article ID 67Google Scholar - Dorić D, Kadelburg Z, Radenović S: A note on occasionally weakly compatible mappings and common fixed points.
*Fixed Point Theory*2012, 13(2):475-480.MathSciNetGoogle Scholar - Alghamdi MA, Radenović S, Shahzad N: On some generalizations of commuting mappings.
*Abstr. Appl. Anal.*2012., 2012: Article ID 952052Google Scholar - Babu GVR, Alemayehu GM: Common fixed point theorems for occasionally weakly compatible maps satisfying property (E. A) using an inequality involving quadratic terms.
*Appl. Math. Lett.*2011, 24: 975-981. 10.1016/j.aml.2011.01.008MathSciNetView ArticleGoogle Scholar - Bhatt A, Chandra H, Sahu DR: Common fixed point theorems for occasionally weakly compatible mappings under relaxed conditions.
*Nonlinear Anal.*2010, 73: 176-182. 10.1016/j.na.2010.03.011MathSciNetView ArticleGoogle Scholar - Ćirić L, Samet B, Vetro C: Common fixed point theorems for families of occasionally weakly compatible mappings.
*Math. Comput. Model.*2011, 53: 631-636. 10.1016/j.mcm.2010.09.015View ArticleGoogle Scholar - Jain MK, Rhoades BE, Saluja AS: Fixed point theorems for occasionally weakly compatible expansive mappings.
*J. Adv. Math. Stud.*2012, 5(2):54-58.MathSciNetGoogle Scholar - Sintunavarat W, Petruşel A, Kumam P:Coupled common fixed point theorems for ${w}^{\ast}$-compatible mappings without mixed monotone property.
*Rend. Circ. Mat. Palermo*2012, 61: 361-383. 10.1007/s12215-012-0096-0MathSciNetView ArticleGoogle Scholar - Abbas, M, Gopal, D, Radenović, S: A note on recently introduced commutative conditions. Indian J. Math. (2011, accepted)Google Scholar
- Imdad M, Ali J, Tanveer M: Remarks on some recent metrical common fixed point theorems.
*Appl. Math. Lett.*2011, 24(7):1165-1169. 10.1016/j.aml.2011.01.045MathSciNetView ArticleGoogle Scholar - Pant V, Pant RP: Common fixed points of conditionally commuting maps.
*Fixed Point Theory*2010, 11(1):113-118.MathSciNetGoogle Scholar - Pant RP, Bisht RK: Occasionally weakly compatible mappings and fixed points.
*Bull. Belg. Math. Soc. Simon Stevin*2012, 19: 1-7.MathSciNetGoogle Scholar - Pant RP: Discontinuity and fixed points.
*J. Math. Anal. Appl.*1999, 240: 284-289. 10.1006/jmaa.1999.6560MathSciNetView ArticleGoogle Scholar - Kannan R: Some results on fixed points.
*Bull. Calcutta Math. Soc.*1968, 60: 71-76.MathSciNetGoogle Scholar - Pant RP, Bisht RK, Arora D: Weak reciprocal continuity and fixed point theorems.
*Ann. Univ. Ferrara*2011, 57(1):181-190. 10.1007/s11565-011-0119-3MathSciNetView ArticleGoogle Scholar - Pant RP, Bisht RK: Common fixed point theorems under a new continuity condition.
*Ann. Univ. Ferrara*2011. 10.1007/s11565-011-0141-5Google Scholar - Gopal D, Imdad M, Abbas M: Metrical common fixed point theorems without completeness and closedness.
*Fixed Point Theory Appl.*2012., 2012: Article ID 18Google Scholar - Pant RP, Bisht RK: Common fixed points of pseudo compatible mappings.
*Rev. R. Acad. Cienc. Exactas Fís. Nat., Ser. A Mat.*2013. 10.1007/s13398-013-0119-5Google Scholar - Pathak HK, Khan MS: A comparison of various types of compatible maps and common fixed points.
*Indian J. Pure Appl. Math.*1997, 28(4):477-485.MathSciNetGoogle Scholar - Pant RP: Common fixed points of Lipschitz type mapping pairs.
*J. Math. Anal. Appl.*1999, 240: 280-283. 10.1006/jmaa.1999.6559MathSciNetView ArticleGoogle Scholar - Pant RP: A common fixed point theorem under a new condition.
*Indian J. Pure Appl. Math.*1999, 30(2):147-152.MathSciNetGoogle Scholar - Rezapour SH, Shahzad N:Common fixed point of $(\psi ,\varphi )$-type contractive maps.
*Appl. Math. Lett.*2011. 10.1016/j.aml.2011.11.004Google Scholar - Matkowski J: Fixed point theorems for mappings with a contractive iterate at a point.
*Proc. Am. Math. Soc.*1977, 62(2):344-348. 10.1090/S0002-9939-1977-0436113-5MathSciNetView ArticleGoogle Scholar - Gopal D, Imdad M, Hasan M, Patel DK: Proving common fixed point theorems for Lipschitz type mappings via absorbing pair.
*Bull. Math. Anal. Appl.*2011, 3(4):92-100. (Erratum: Bull. Math. Anal. Appl. 4(4), 45-46 (2012))MathSciNetGoogle Scholar

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