# Common fixed point theorems for generalized $\mathcal{J}\mathcal{H}$-operator classes and invariant approximations

- Wutiphol Sintunavarat
^{1}and - Poom Kumam
^{1}Email author

**2011**:67

https://doi.org/10.1186/1029-242X-2011-67

© Sintunavarat and Kumam; licensee Springer. 2011

**Received: **30 March 2011

**Accepted: **22 September 2011

**Published: **22 September 2011

## Abstract

In this article, we introduce two new different classes of noncommuting selfmaps. The first class is more general than $\mathcal{J}\mathcal{H}$-operator class of Hussain et al. (Common fixed points for $\mathcal{J}\mathcal{H}$-operators and occasionally weakly biased pairs under relaxed conditions. Nonlinear Anal. **74**(6), 2133-2140, 2011) and occasionally weakly compatible class. We establish the existence of common fixed point theorems for these classes. Several invariant approximation results are obtained as applications. Our results unify, extend, and complement several well-known results.

**2000 Mathematical Subject Classification:** 47H09; 47H10.

### Keywords

common fixed point occasionally weakly compatible maps Banach operator pair $\mathcal{P}$-operator pair $\mathcal{J}\mathcal{H}$-operator pair generalized $\mathcal{J}\mathcal{H}$-operator pair invariant approximation## 1. Introduction

The fixed point theorem, generally known as the Banach contraction principle, appeared in explicit form in Banach's thesis in 1922 [1], where it was used to establish the existence of a solution for an integral equation. Since its simplicity and usefulness, it has become a very popular tool in solving existence problems in many branches of mathematical analysis. Banach contraction principle has been extended in many different directions. Many authors established fixed point theorems involving more general contractive conditions.

In 1976, Jungck [2] extend the Banach contraction principle to a common fixed point theorem for commuting maps. Sessa [3] defined the notion of weakly commuting maps and established a common fixed point for this maps. Jungck [4] coined the term compatible mappings to generalize the concept of weak commutativity and showed that weakly commuting maps are compatible but the converse is not true. Afterward, many authors studied about common fixed point theorems for noncommuting maps (see [5–14]).

In 1996, Al-Thagafi [15] established some theorems on invariant approximations for commuting maps. Shahzad [16], Al-Thagafi and Shahzad [17, 18], Hussain and Jungck [19], Hussain [20], Hussain and Rhoades [21], Jungck and Hussain [22], O'Regan and Hussain [23], and Pathak and Hussain [24] extended the result of Al-Thagafi [15] and Ciric [25] for pointwise *R*-subweakly commuting maps, compatible maps, *C*_{
q
} -commuting maps, and Banach operator pairs. Pathak and Hussain [26] introduced two new classes of noncommuting selfmaps, so-called $\mathcal{P}$-operator and $\mathcal{P}$-suboperator pair class. Recently, Hussain et al. [27] introduced $\mathcal{J}\mathcal{H}$-operator and occasionally weakly *g*-biased class which are more general than above classes and established common fixed point theorems for these class.

In this article shall introduce two new classes of noncommuting selfmaps. First class, generalized $\mathcal{J}\mathcal{H}$-operator class, contains $\mathcal{J}\mathcal{H}$-operator classes of Hussain et al. [27] and occasionally weakly compatible classes. Second class is the so-called generalized $\mathcal{J}\mathcal{H}$-suboperator class. We will be present some common fixed point theorems for these classes and the existence of the common fixed points for best approximation. Our results improve, extend, and complement all the results in literature.

## 2. Preliminaries

Let *M* be a subset of a norm space *X*. We shall use *cl*(*A*) and *wcl*(*A*) to denote the closure and the weak closure of a set *A*, respectively, and *d*(*x*, *A*) to denote inf{||*x*-*y*|| : *y* ∈ *A*} where *x* ∈ *X* and *A* ⊆ *X*. Let *f* and *T* be selfmaps of *M*. A point *x* ∈ *M* is called a *fixed point* of *f* if *fx* = *x*. The set of all fixed points of *f* is denoted by *F*(*f*). A point *x* ∈ *M* is called a *coincidence point* of *f* and *T* if *fx* = *Tx*. We shall call *w* = *fx* = *Tx* a *point of coincidence* of *f* and *T*. A point *x* ∈ *M* is called a *common fixed point* of *f* and *T* if *x* = *fx* = *Tx*. Let *C*(*f*, *T*), *PC*(*f*, *T*), and *F*(*f*, *T*) denote the sets of all coincidence points, points of coincidence, and common fixed points, respectively, of the pair (*f*, *T*).

The map *T* is called *contraction* [resp. *f-contraction*] on *M* if ||*Tx*-*Ty*|| ≤ *k*||*x*-*y*|| [resp. ||*Tx* - *Ty*|| ≤ *k*||*fx* - *fy*||] for all *x*, *y* ∈ *M* and for some *k* ∈ [0, 1). The map *T* is called *nonexpansive* [resp. *f-nonexpansive*] on *M* if ||*Tx* - *Ty*|| ≤ ||*x* - *y*|| [resp. ||*Tx* - *Ty*|| ≤ ||*fx* - *fy*||] for all *x*, *y* ∈ *M*. The pair (*f*, *T*) is called:

**(i):** *commuting* if *Tfx* = *fTx* for all *x* ∈ *M*;

**(ii):**

*R-weakly commuting*[8] if for all

*x*∈

*M*, there exists

*R >*0 such that

If *R* = 1, then the maps are called *weakly commuting*;

**(iii):**

*compatible*[28] if $\underset{n\to \infty}{lim}\parallel Tf{x}_{n}-fT{x}_{n}\parallel \phantom{\rule{0.3em}{0ex}}=0$ when {

*x*

_{ n }} is a sequence such that

for some *t* ∈ *M*;

**(iv):** *weakly compatible*[29] if *Tfx* = *fTx* for all *x* ∈ *C*(*f*, *T*);

**(v):** *occasionally weakly compatible*[18, 30] if *fTx* = *Tfx* for some *x* ∈ *C*(*f*, *T*);

**(vi):** *Banach operator pair*[31] if *f*(*F*(*T*)) ⊆ *F*(*T*);

**(vii):**$\mathcal{P}$-*operator*[26] if ||*u* - *Tu*|| ≤ diam (*C*(*f*, *T*)) for some *u* ∈ *C*(*f*, *T*);

**(viii):**$\mathcal{J}\mathcal{H}$-

*operator*[27] if there exist a point

*w*=

*fx*=

*Tx*in

*PC*(

*f*,

*T*) such that

The set *M* is called *convex* if *kx* + (1 - *k*)*y* ∈ *M* for all *x*, *y* ∈ *M* and all *k* ∈ [0, 1]; and *q-starshaped* with *q* ∈ *M* if the segment [*q*, *x*] = {*kx* + (1 - *k*)*q* : *k* ∈ [0, 1]} joining *q* to *x* is contained to *M*. The map *f* : *M* → *M* is called *affine* if *M* is convex and *f*(*kx* + (1 - *k*)*y*) = *kfx* + (1 - *k*)*fy* for all *x*, *y* ∈ *M* and all *k* ∈ [0, 1]; and *q-affine* if *M* is *q*-starshaped and *f*(*kx* + (1 - *k*)*q*) = *kfx* + (1 - *k*)*fq* for all *x*, *y* ∈ *M* and all *k* ∈ [0, 1].

A map *T* : *M* → *X* is said to be *semicompact* if a sequence {*x*_{
n
} } in *M* such that (*x*_{
n
} - *Tx*_{
n
} ) → 0 has a subsequence {*x*_{
j
} } in *M* such that *x*_{
j
} → *z* for some *z* ∈ *M*. Clearly if *cl*(*T*(*M*)) is compact, then *T*(*M*) is complete, *T*(*M*) is bounded, and *T* is semicompact. The map *T* : *M* → *X* is said to be *weakly semicompact* if a sequence {*x*_{
n
} } in *M* such that (*x*_{
n
} - *Tx*_{
n
} ) → 0 has a subsequence {*x*_{
j
} } in *M* such that *x*_{
j
} → *z* weakly for some *z* ∈ *M*. The map *T* : *M* → *X* is said to be *demiclosed* at 0 if, for every sequence {*x*_{
n
} } in *M* converging weakly to *x* and {*Tx*_{
n
} } converges to 0 ∈ *X*, then *Tx* = 0.

## 3. Generalized $\mathcal{J}\mathcal{H}$-operator classes

We begin this section by introduce a new noncommuting class.

**Definition 3.1**. Let

*f*and

*T*be selfmaps of a normed space

*X*. The order pair (

*f*,

*T*) is called a

*generalized*$\mathcal{J}\mathcal{H}$-

*operator with order n*if there exists a point

*w*=

*fx*=

*Tx*in

*PC*(

*f*,

*T*) such that

for some *n* ∈ ℕ.

It is obvious that a $\mathcal{J}\mathcal{H}$-operator pair (*f*, *T*) is generalized $\mathcal{J}\mathcal{H}$-operator with order *n*. But the converse is not true in general, see Example 3.2.

**Example 3.2**. Let

*X*= ℝ with usual norm and

*M*= [0, ∞). Define

*f*,

*T*:

*M*→

*M*by

Then *C*(*f*, *T*) = {0, 2} and *PC*(*f*, *T*) = {3, 5}. Obvious (*f*, *T*) is a generalized $\mathcal{J}\mathcal{H}$-operator with order *n* ≥ 2 but not a $\mathcal{J}\mathcal{H}$-operator and so not a occasionally weakly compatible and not weakly compatible. Moreover, note that *F*(*T*) = {1} and *f* 1 = 2 ∉ *F*(*T*) which implies that (*f*, *T*) is not a Banach operator pair.

**Theorem 3.3**.

*Let f and T be selfmaps of a nonempty subset M of a normed space X and*(

*f*,

*T*)

*be a generalized*$\mathcal{J}\mathcal{H}$-

*operator with order n on M. If f and T satisfying the following condition:*

*for all x*, *y* ∈ *M and* 0 ≤ *k <* 1, *then f and T have a unique common fixed point*.

*Proof*. By the notation of generalized $\mathcal{J}\mathcal{H}$-operator, we get that there exists a point

*w*∈

*M*such that

*w*=

*fx*=

*Tx*and

*n*∈ ℕ. Suppose there exists another point

*y*∈

*M*for which

*z*=

*fy*=

*Ty*. Then from (3.2), we get

*k <*1, the inequality (3.4) implies that ||

*Tx*-

*Ty*|| = 0, which, in turn implies that

*w*=

*fx*=

*Tx*=

*z*. Therefore, there exists a unique element

*w*in

*M*such that

*w*=

*fx*=

*Tx*. So diam(

*PC*(

*f*,

*T*)) = 0. Using (3.3), we have

Thus *w* = *x*, that is *x* is a unique common fixed point of *f* and *T*. □

**Definition 3.4**. Let

*M*be a

*q*-starshaped subset of a normed space

*X*and

*f*,

*T*selfmaps of a normed space

*M*. The order pair (

*f*,

*T*) is called a

*generalized*$\mathcal{J}\mathcal{H}$-

*suboperator with order n*if for each

*k*∈ [0, 1], (

*f*,

*T*

_{ k }) is a generalized $\mathcal{J}\mathcal{H}$-operator with order

*n*that is, for

*k*∈ [0, 1] there exists a point

*w*=

*fx*=

*T*

_{ k }

*x*in

*PC*(

*f*,

*T*

_{ k }) such that

for some *n* ∈ ℕ, where *T*_{
k
} is selfmap of *M* such that *T*_{
k
}*x* = *kTx* + (1 - *k*)*q* for all *x* ∈ *M*.

Clearly, a generalized $\mathcal{J}\mathcal{H}$-suboperator with order *n* is generalized $\mathcal{J}\mathcal{H}$-operator with order *n* but the converse is not true in general, see Example 3.5.

**Example 3.5**. Let

*X*= ℝ with usual norm and

*M*= [0, ∞). Define

*f*,

*T*:

*M*→

*M*(see Example 3.2). Then

*M*is

*q*-starshaped for

*q*= 0 and

*C*(

*f*,

*T*) = {0, 2}, $C\left(f,{T}_{k}\right)=\left\{\frac{2}{k}\right\}$, and $PC\left(f,{T}_{k}\right)=\left\{\frac{4}{k}\right\}$ for

*k*∈ (0, 1). Obvious (

*f*,

*T*) is a generalized $\mathcal{J}\mathcal{H}$-operator with

*n*= 2 but not a generalized $\mathcal{J}\mathcal{H}$-suboperator for every

*n*∈ ℕ as

for each *k* ∈ (0, 1).

**Theorem 3.6**.

*Let f and T be selfmaps on a q-starshaped subset M of a normed space X. Assume that f is q-affine*, (

*f*,

*T*)

*is a generalized*$\mathcal{J}\mathcal{H}$-

*suboperator with order n*

_{0},

*and for all x*,

*y*∈

*M*,

*Then F*(*f*, *T*) ≠ ∅ *if one of the following conditions holds:*

**(a):** *cl*(*T*(*M*)) *is compact and f and T are continuous;*

**(b):** *wcl*(*T*(*M*)) *is weakly compact, f is weakly continuous and* (*f* - *T*) *is demiclosed at* 0;

**(c):** *T*(*M*) *is bounded, T is semicompact and f and T are continuous;*

**(d):** *T*(*M*) *is bounded, T is weakly semicompact, f is weakly continuous and* (*f* - *T*) *is demiclosed at* 0.

*Proof*. Let {

*k*

_{ n }} ⊆ (0, 1) such that

*k*

_{ n }→ 1 as

*n*→ ∞. For

*n*∈ ℕ, we define

*T*

_{ n }:

*M*→

*M*by

*T*

_{ n }

*x*=

*k*

_{ n }

*Tx*+ (1 -

*k*

_{ n })

*q*for all

*x*∈

*M*. Since (

*f*,

*T*) is a generalized $\mathcal{J}\mathcal{H}$-suboperator with order

*n*

_{0}, (

*f*,

*T*

_{ n }) is a generalized $\mathcal{J}\mathcal{H}$-operator order

*n*

_{0}for all

*n*∈ ℕ. Using inequality (3.7) it follows that

for all *x*, *y* ∈ *M*. By Theorem 3.3, there exists *x*_{
n
} ∈ *M* such that *x*_{
n
} = *fx*_{
n
} = *T*_{
n
}*x*_{
n
} for every *n* ∈ ℕ.

*cl*(

*T*(

*M*)) is compact, there exists a subsequence {

*Tx*

_{ m }} of {

*Tx*

_{ n }} such that $\underset{m\to \infty}{lim}T{x}_{m}=y$ for some

*y*∈

*M*. By the definition of

*T*

_{ m }, we get

Since *f* and *T* are continuous, *y* = *fy* = *Ty* that is *y* ∈ *F*(*f*, *T*) and then *F*(*f*, *T*) ≠ ∅.

(b): From weakly compact of *wcl*(*T*(*M*)) there exist a subsequence {*x*_{
m
} } of {*x*_{
n
} } in *M* converging weakly to *y* ∈ *M* as *m* → ∞. Since *f* is weakly continuous, *fy* = *y* that is $\underset{m\to \infty}{lim}\left(f{x}_{m}-T{x}_{m}\right)=0$. It follows from (*f* - *T*) is demiclosed at 0 and $\underset{m\to \infty}{lim}\left(f{x}_{m}-T{x}_{m}\right)=0$ that *fy* - *Ty* = 0. Therefore, *y* = *fy* = *Ty* that is *F*(*f*, *T*) ≠ ∅.

*T*(

*M*) is bounded,

*k*

_{ n }→ 1, and

*n*∈ ℕ, we get $\underset{m\to \infty}{lim}\left({x}_{n}-T{x}_{n}\right)=0$. As

*T*is semicompact, there exist a subsequence {

*x*

_{ m }} of {

*x*

_{ n }} in

*M*such that $\underset{m\to \infty}{lim}{x}_{m}=y$ for some

*y*∈

*M*. By definition of

*T*

_{ m }, we get

By the continuous of both *f* and *T*, we have *y* = *fy* = *Ty*. Therefore *F*(*f*, *T*) ≠ ∅.

(d): Similarly case (c), we have $\underset{m\to \infty}{lim}\left({x}_{n}-T{x}_{n}\right)=0$. Since *T* is weakly semicompact, there exist a subsequence {*x*_{
m
} } of {*x*_{
n
} } in *M* such that converging weakly to *y* ∈ *M* as *m* → ∞. By weak continuity of *f*, we get *fy* = *y*. It follows from $\underset{m\to \infty}{lim}\left(f{x}_{m}-T{x}_{m}\right)=\underset{m\to \infty}{lim}\left({x}_{m}-T{x}_{m}\right)=0$, *x*_{
m
} converging weakly to *y*, and *f* - *T* is demiclosed at 0 that (*f* - *T*)(*y*) = 0 which implies that *fy* = *Ty*. Therefore *y* = *fy* = *Ty* and hence *y* ∈ *F*(*f*, *T*).

□

**Remark 3.7**. We can replace assumption of *f* being *q*-affine by *q* ∈ *F*(*f*) and *f*(*M*) = *M* in Theorem 3.6.

If *f* is identity mapping in Theorem 3.6, then we get the following corollary.

**Corollary 3.8**.

*Let T be selfmaps on a q-starshaped subset M of a normed space X. Assume that for all x*,

*y*∈

*M*,

*Then F*(*T*) ≠ ∅ *if one of the following conditions holds:*

(a): *cl*(*T*(*M*)) *is compact and T is continuous;*

(b): *wcl*(*T*(*M*)) *is weakly compact and* (*I* - *T*) *is demiclosed at* 0, *where I is identity on M;*

(c): *T*(*M*) *is bounded, T is semicompact and T is continuous;*

(d): *T*(*M*) *is bounded, T is weakly semicompact and* (*I* - *T*) *is demiclosed at* 0, *where I is identity on M*.

## 4. Invariant approximations

*M*is a subset of a normed space

*X*and

*p*∈

*X*, let

The set *B*_{
M
} (*p*) is called the set of best approximants to *p* ∈ *X* out of *M*. Let ${\mathcal{C}}_{0}$ denote the class of closed convex subsets *M* of *X* containing 0. It is known that *B*_{
M
} (*p*) is closed, convex, and contained in ${M}_{p}\in {\mathcal{C}}_{0}$.

**Theorem 4.1**.

*Let M be a subset of a normed space X, f and T be selfmaps of X with T*(∂

*M*∩

*M*) ⊆

*M, p*∈

*F*(

*f*,

*T*),

*B*

_{ M }(

*p*)

*be a closed q-starshaped. Assume that f*(

*B*

_{ M }(

*p*)) =

*B*

_{ M }(

*p*),

*q*∈

*F*(

*f*), (

*f*,

*T*)

*is a generalized*$\mathcal{J}\mathcal{H}$-

*suboperator with order n*

_{0}

*on B*

_{ M }(

*p*),

*and for all x*,

*y*∈

*B*

_{ M }(

*p*) ∪ {

*p*},

*If cl*(*T*(*B*_{
M
} (*p*))) *is compact, f and T are continuous on B*_{
M
} (*p*), *then F* (*f*, *T* )∩*B*_{
M
}(*p*) ≠ ∅.

*Proof*. Let *x* ∈ *B*_{
M
} (*p*). It follows from ||*kx* + (1 - *k*)*p* - *p*)|| = *k*||*x* - *p*|| *< d*(*p*, *M*) for all *k* ∈ (0, 1) that {*kx*+(1 - *k*)*p* : *k* ∈ (0, 1)}∩*M* ≠ ∅ which implies that *x* ∈ ∂*M* ∩ *M*. So *B*_{
M
} (*p*) ⊆ ∂*M* ∩ *M* and hence *T*(*B*_{
M
} (*p*)) ⊆ *T* (∂*M* ∩ *M* ). As *T* (∂*M* ∩ *M* ) ⊆ *M* that *T*(*B*_{
M
} (*p*)) ⊆ *M*. Now the result follows from Theorem 3.6 (*a*) with *M* = *B*_{
M
} (*p*). Therefore, *F*(*f*, *T*) ∩ *B*_{
M
} (*p*) ≠ ∅. □

**Theorem 4.2**.

*Let M be a subset of a normed space X, f and T be selfmaps of X with T*(∂

*M*∩

*M*) ⊆

*M, p*∈

*F*(

*f*,

*T*), ${C}_{M}^{f}\left(p\right)$

*be a closed q-starshaped. Assume that*$f\left({C}_{M}^{f}\left(p\right)\right)={C}_{M}^{f}\left(p\right)$,

*q*∈

*F*(

*f*), (

*f*,

*T*)

*is a generalized*$\mathcal{J}\mathcal{H}$ -

*suboperator with order n*

_{0}

*on*${C}_{M}^{f}\left(p\right)$,

*and for all*$x,y\in {C}_{M}^{f}\left(p\right)\cup \left\{p\right\}$,

*If*$cl\left(T\left({C}_{M}^{f}\left(p\right)\right)\right)$*is compact, f and T are continuous on*${C}_{M}^{f}\left(p\right)$, *then F* (*f*, *T*)∩*B*_{
M
} (*p*) ≠ ∅.

*Proof*. Let $x\in {C}_{M}^{f}\left(p\right)$. By definition of ${C}_{M}^{f}\left(p\right)$ and $f\left({C}_{M}^{f}\left(p\right)\right)={C}_{M}^{f}\left(p\right)$, we have ${C}_{M}^{f}\left(p\right)\subseteq {B}_{M}\left(p\right)$. Using the same argument in the proof of Theorem 4.1 shows that there exists *x* ∈ ∂*M* ∩ *M*. It follows from *T*(∂*M* ∩ *M*) ⊆ *f*(*M*) ∩ *M* that *Tx* ∈ *f*(*M*). Therefore, we can find a point *z* ∈ *M* such that *Tx* = *fz*. Thus $z\in {C}_{M}^{f}\left(p\right)$ which implies that $T\left({C}_{M}^{f}\left(p\right)\right)\subseteq f\left({C}_{M}^{f}\left(p\right)\right)={C}_{M}^{f}\left(p\right)$. Now the result follows from Theorem 3.6 (*a*) with $M={B}_{M}^{f}\left(p\right)$. Therefore, we have *F* (*f*, *T*) ∩ *B*_{
M
} (*p*) ≠ ∅. □

**Theorem 4.3**.

*Let M be a subset of a normed space X, f and T be selfmaps of X with T*(∂

*M*∩

*M*) ⊆

*M, p*∈

*F*(

*f*,

*T*),

*B*

_{ M }(

*p*)

*be a weakly closed and q-starshaped. Assume that f*(

*B*

_{ M }(

*p*)) =

*B*

_{ M }(

*p*),

*q*∈

*F*(

*f*), (

*f*,

*T*)

*is a generalized*$\mathcal{J}\mathcal{H}$-

*suboperator with order n*

_{0}

*on B*

_{ M }(

*p*),

*and for all x*,

*y*∈

*B*

_{ M }(

*p*) ∪ {

*p*},

*If wcl*(*T*(*B*_{
M
}(*p*))) *is weakly compact, f is weakly continuous on B*_{
M
}(*p*) *and* (*f* - *T*) *is demiclosed at* 0, *then F*(*f*, *T*) ∩ *B*_{
M
}(*p*) ≠ ∅.

*Proof*. We use an argument similar to that in Theorem 4.1 and apply Theorem 3.6 (*b*) instead of Theorem 3.6 (*a*). □

**Theorem 4.4**.

*Let M be a subset of a normed space X, f and T be selfmaps of X with T*(∂

*M*∩

*M*) ⊆

*M, p*∈

*F*(

*f*,

*T*), ${C}_{M}^{f}\left(p\right)$

*be a weakly closed and q-starshaped. Assume that*$f\left({C}_{M}^{f}\left(p\right)\right)={C}_{M}^{f}\left(p\right)$,

*q*∈

*F*(

*f*), (

*f*,

*T*)

*is a generalized*$\mathcal{J}\mathcal{H}$-

*suboperator with order n*

_{0}

*on*${C}_{M}^{f}\left(p\right)$,

*and for all*$x,y\in {C}_{M}^{f}\left(p\right)\cup \left\{p\right\}$,

*If*$wcl\left(T\left({C}_{M}^{f}\left(p\right)\right)\right)$*is weakly compact, f is weakly continuous on*${C}_{M}^{f}\left(p\right)$*and* (*f* - *T*) *is* *demiclosed at* 0, *then F*(*f*, *T*) ∩ *B*_{
M
}(*p*) ≠ ∅.

*Proof*. We use an argument similar to that in Theorem 4.2 and apply Theorem 3.6 (*b*) instead of Theorem 3.6 (*a*). □

**Theorem 4.5**.

*Let M be a subset of a normed space X, f and T be selfmaps of X, p*∈

*F*(

*f*,

*T*), $M\in {\mathcal{C}}_{0}$

*with T*(

*M*

_{ p }) ⊆

*f*(

*M*) ⊆

*M. Assume that*||

*fx*-

*p*|| = ||

*x*-

*p*||

*for all x*∈

*M and for all x*,

*y*∈

*M*

_{ p }∪ {

*p*},

*If cl*(

*f*(

*M*

_{ p }))

*is compact, then B*

_{ M }(

*p*)

*is nonempty, closed, and convex and T*(

*B*

_{ M }(

*p*)) ⊆

*f*(

*B*

_{ M }(

*p*)) ⊆

*B*

_{ M }(

*p*).

*If in addition, for all x*,

*y*∈

*BM*(

*p*),

*then F*(*f*) ∩ *B*_{
M
} (*p*) ≠ ∅ *and F*(*T*) ∩ *B*_{
M
} (*p*) ≠ ∅. *Moreover, F*(*f*, *T*) ∩ *B*_{
M
} (*p*) ≠ ∅ *if for some q* ∈ *B*_{
M
} (*p*), *f is q-affine and* (*f*, *T*) *is a generalized*$\mathcal{J}\mathcal{H}$*suboperator with order n on B*_{
M
} (*p*).

*Proof*. Assume that

*p*∉

*M*. If

*u*∈

*M*\

*M*

_{ p }, then ||

*u*||

*>*2||

*p*||. Since 0 ∈

*M*, we get

*α*:=

*d*(

*p*,

*M*

_{ p }) =

*d*(

*p*,

*M*). As

*cl*(

*f*(

*M*

_{ p })) is compact and the norm is continuous that there exists

*z*∈

*cl*(

*f*(

*M*

_{ p })) such that

*β*:=

*d*(

*p*,

*cl*(

*f*(

*M*

_{ p }))) = ||

*z*-

*p*||. So we have

*y*∈

*M*

_{ p }. Therefore,

*α*=

*β*and

*B*

_{ M }(

*p*) is nonempty closed and convex such that

*f*(

*B*

_{ M }(

*p*)) ⊆

*B*

_{ M }(

*p*). Next step, we show that

*T*(

*B*

_{ M }(

*p*)) ⊆

*f*(

*B*

_{ M }(

*p*)). Suppose that

*w*∈

*T*(

*B*

_{ M }(

*p*)). It follows from

*T*(

*B*

_{ M }(

*p*)) ⊆

*T*(

*M*

_{ p }) ⊆

*f*(

*M*) that there exists

*w*

_{1}∈

*M*

_{ p }and

*w*

_{2}∈

*M*such that

*w*=

*Tw*

_{1}=

*fw*

_{2}. Using the condition (4.5), we have

*w*

_{2}∈

*B*

_{ M }(

*p*) and

*w*

_{1}∈

*f*(

*B*

_{ M }(

*p*)) which implies that

*T*(

*B*

_{ M }(

*p*)) ⊆

*f*(

*B*

_{ M }(

*p*)) ⊆

*B*

_{ M }(

*p*). Now, suppose that

*f*satisfies inequality (4.6) on

*B*

_{ M }(

*p*). Therefore, the condition (4.5) on

*M*

_{ p }∪ {

*p*} implies that

for all *x*, *y* ∈ *B*_{
M
} (*p*). Since *f* (*M*_{
p
} ) is compact, *f* (*B*_{
M
} (*p*)) and *T* (*B*_{
M
} (*p*)) are compact. Moreover, *f*(*B*_{
M
} (*p*)) ⊆ *B*_{
M
} (*p*) and *T* (*B*_{
M
} (*p*)) ⊆ *B*_{
M
} (*p*). It follows from Corollary 3.8 that *F*(*f*) ∩ *B*_{
M
} (*p*) ≠ ∅ and *F*(*T*) ∩ *BM* (*p*) ≠ ∅. Finally, we follow from Theorem 3.6 by replacing *M* with *B*_{
M
} (*p*). □

**Theorem 4.6**.

*Let M be a subset of a normed space X, f and T be selfmaps of X, p*∈

*F*(

*f*,

*T*), $M\in {\mathcal{C}}_{0}$

*with T*(

*M*

_{ p }) ⊆

*f*(

*M*) ⊆

*M. Assume that*||

*fx*-

*p*|| = ||

*x*-

*p*||

*for all x*∈

*M and for all x*,

*y*∈

*M*

_{ p }∪ {

*p*},

*If cl*(

*T*(

*M*

_{ p }))

*is compact, then B*

_{ M }(

*p*)

*is nonempty, closed, convex, and T*(

*B*

_{ M }(

*p*)) ⊆

*f*(

*B*

_{ M }(

*p*)) ⊆

*B*

_{ M }(

*p*).

*If in addition, for all x*,

*y*∈

*B*

_{ M }(

*p*),

*then F*(*T*) ∩ *B*_{
M
} (*p*) ≠ ∅. *Moreover, F*(*f*, *T*) ∩ *B*_{
M
} (*p*) ≠ ∅ *if for some q* ∈ *B*_{
M
} (*p*), *f is q-affine and* (*f*, *T*) *is a generalized*$\mathcal{J}\mathcal{H}$*suboperator with order n on B*_{
M
} (*p*).

*Proof*. We can obtain the result by using an argument similar to that in Theorem 4.5.

□

**Theorem 4.7**.

*Let M be a subset of a Banach space X, f and T be selfmaps of X, p*∈

*F*(

*f*,

*T*), $M\in {\mathcal{C}}_{0}$

*with T*(

*Mp*) ⊆

*f*(

*M*) ⊆

*M. Assume that*||

*fx*-

*p*|| = ||

*x*-

*p*||

*for all x*∈

*M and for all x*,

*y*∈

*M*

_{ p }∪ {

*p*},

*If wcl*(

*f*(

*M*

_{ p }))

*is weakly compact and*(

*f*-

*T*)

*is demiclosed at*0,

*then B*

_{ M }(

*p*)

*is nonempty, (weakly) closed, and convex and T*(

*B*

_{ M }(

*p*)) ⊆

*f*(

*B*

_{ M }(

*p*)) ⊆

*B*

_{ M }(

*p*).

*If, in addition, for all x*,

*y*∈

*B*

_{ M }(

*p*),

*then F*(*f*) ∩ *B*_{
M
} (*p*) ≠ ∅ *and F*(*T*) ∩ *B*_{
M
} (*p*) ≠ ∅. *Moreover, F*(*f*, *T*) ∩ *B*_{
M
} (*p*) ≠ ∅ *if for some q* ∈ *B*_{
M
} (*p*), *f is q-affine, weakly continuous on B*_{
M
} (*p*) *and* (*f*, *T*) *is a generalized*$\mathcal{J}\mathcal{H}$*suboperator with order n on B*_{
M
} (*p*).

*Proof*. To obtain the result, we use an argument similar to that in Theorem 4.5 and apply Theorem 3.6 (*b*) instead of Theorem 3.6(a), respectively. Finally, we use Lemma 5.5 of Singh et al. [33] with *f*(*x*) = ||*x* - *p*|| and *C* = *wcl*(*T*(*M*_{
p
} )) to show that there exists *z* ∈ *C* such that *d*(*p*, *C*) = ||*z* - *p*||. □

**Theorem 4.8**.

*Let M be a subset of a Banach space X, f and T be selfmaps of X, p*∈

*F*(

*f*,

*T*), $M\in {\mathcal{C}}_{0}$

*with T*(

*M*

_{ p }) ⊆

*f*(

*M*) ⊆

*M. Assume that*||

*fx*-

*p*|| = ||

*x*-

*p*||

*for all x*∈

*M and for all x*,

*y*∈

*M*

_{ p }∪ {

*p*},

*If wcl*(

*f*(

*M*

_{ p }))

*is weakly compact and*(

*f*-

*T*)

*is demiclosed at*0,

*then B*

_{ M }(

*p*)

*is nonempty, (weakly) closed, and convex and T*(

*B*

_{ M }(

*p*)) ⊆

*f*(

*BM*(

*p*)) ⊆

*B*

_{ M }(

*p*).

*If in addition, for all x*,

*y*∈

*B*

_{ M }(

*p*),

*then F*(*T*) ∩ *B*_{
M
} (*p*) ≠ ∅. *Moreover, F*(*f*, *T*) ∩ *B*_{
M
} (*p*) ≠ ∅ *if for some q* ∈ *B*_{
M
} (*p*), *f is q-affine, weakly continuous on B*_{
M
} (*p*) *and* (*f*, *T*) *is a generalized*$\mathcal{J}\mathcal{H}$*suboperator with order n on B*_{
M
} (*p*).

*Proof*. We can obtain the result using an argument similar to that in Theorem 4.7. □

## Declarations

### Acknowledgements

Mr. Wutiphol Sintunavarat would like to thank the Research Professional Development Project Under the Science Achievement Scholarship of Thailand (SAST) and the Faculty of Science, KMUTT for financial support during the preparation of this manuscript for Ph.D. Program at KMUTT. The second author was supported by the Commission on Higher Education, the Thailand Research Fund and the King Mongkut's University of Technology Thonburi (KMUTT) (Grant No.MRG5380044).

Moreover, we also would like to thank the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission for financial support (Grant No. 54000267). Special thanks are also due to the reviewer, who have made a number of valuable comments and suggestions which have improved the manuscript greatly.

## Authors’ Affiliations

## References

- Banach S:
**Sur les opérations dans les ensembles abstraits et leurs applications aux équations intégrales.***Fund Math*1922,**3:**133–181.MATHGoogle Scholar - Jungck G:
**Commuting mappings and fixed points.***Am Math Monthly*1976,**83:**261–263. 10.2307/2318216MathSciNetView ArticleMATHGoogle Scholar - Sessa S:
**On a weak commutativity condition of mappings in fixed point considerations.***Publ Inst Math (Beograd) (N.S.)*1982,**32**(46):149–153.MathSciNetMATHGoogle Scholar - Jungck G:
**Compatible mappings and common fixed points.***Int J Math Math Sci*1986,**9:**771–779. 10.1155/S0161171286000935MathSciNetView ArticleMATHGoogle Scholar - Kang SM, Cho CL, Jungck G:
**Common fixed point of compatible mappings.***Int J Math Math Sci*1990,**13:**61–66. 10.1155/S0161171290000096MathSciNetView ArticleMATHGoogle Scholar - Kang SM, Ryu JW:
**A common fixed point theorem for compatible mappings.***Math Jpn*1990,**35:**153–157.MathSciNetMATHGoogle Scholar - Mongkolkeha C, Kumam P:
**Fixed point and common fixed point theorems for generalized weak contraction mappings of integral type in modular spaces.***Int J Math Math Sci*2011,**2011:**12. Article ID 705943MathSciNetView ArticleMATHGoogle Scholar - Pant RP:
**Common fixed points of noncommuting mappings.***J Math Anal Appl*1994,**188:**436–440. 10.1006/jmaa.1994.1437MathSciNetView ArticleMATHGoogle Scholar - Pathak HK, Cho YJ, Kang SM:
**Common fixed points of biased maps of type (A) and application.***Int J Math Math Sci*1998,**21:**681–694. 10.1155/S0161171298000945MathSciNetView ArticleMATHGoogle Scholar - Sintunavart W, Kumam P:
**Coincidence and common fixed points for hybrid strict contractions without the weakly commuting condition.***Appl Math Lett*2009,**22:**1877–1881. 10.1016/j.aml.2009.07.015MathSciNetView ArticleMATHGoogle Scholar - Sintunavart W, Kumam P:
**Weak condition for generalized multi-valued (**f**,**α**,**β**)-weak contraction mappings.***Appl Math Lett*2011,**24:**460–465. 10.1016/j.aml.2010.10.042MathSciNetView ArticleGoogle Scholar - Sintunavart W, Kumam P:
**Coincidence and common fixed points for generalized contraction multi-valued mappings.***J Comput Anal Appl*2011,**13**(2):362–367.MathSciNetMATHGoogle Scholar - Sintunavart W, Kumam P:
**Gregus-type common fixed point theorems for tangential multivalued mappings of integral type in metric spaces.***Int J Math Math Sci*2011,**2011:**12. Article ID 923458MathSciNetMATHGoogle Scholar - Sintunavart W, Kumam P:
**Gregus type fixed points for a tangential multi-valued mappings satisfying contractive conditions of integral type.***J Inequal Appl*2011,**2011:**3. 10.1186/1029-242X-2011-3View ArticleMathSciNetMATHGoogle Scholar - Al-Thagafi MA:
**Common fixed points and best approximation.***J Approx Theory*1996,**85:**318–323. 10.1006/jath.1996.0045MathSciNetView ArticleMATHGoogle Scholar - Shahzad N:
**Invariant approximations and R-subweakly commuting maps.***J Math Anal Appl*2001,**257:**39–45. 10.1006/jmaa.2000.7274MathSciNetView ArticleMATHGoogle Scholar - Al-Thagafi MA, Shahzad N:
**Noncommuting selfmaps and invariant approximations.***Nonlinear Anal*2006,**64:**2778–2786. 10.1016/j.na.2005.09.015MathSciNetView ArticleMATHGoogle Scholar - Al-Thagafi MA, Shahzad N:
**Generalized I-nonexpansive selfmaps and invariant approximations.***Acta Math Sinica*2008,**24:**867–876. 10.1007/s10114-007-5598-xMathSciNetView ArticleMATHGoogle Scholar - Hussain N, Jungck G:
**Common fixed point and invariant approximation results for noncommuting generalized (**f**,**g**)-nonexpansive maps.***J Math Anal Appl*2006,**321:**851–861. 10.1016/j.jmaa.2005.08.045MathSciNetView ArticleMATHGoogle Scholar - Hussain N:
**Common fixed points in best approximation for Banach operator pairs with Ciric Type I-contractions.***J Math Anal Appl*2008,**338:**1351–1363. 10.1016/j.jmaa.2007.06.008MathSciNetView ArticleMATHGoogle Scholar - Hussain N, Rhoades BE: C
_{ q }**-commuting maps and invariant approximations.***Fixed Point Theory Appl*2006,**2006:**9.MathSciNetMATHGoogle Scholar - Jungck G, Hussain N:
**Compatible maps and invariant approximations.***J Math Anal Appl*2007,**325:**1003–1012. 10.1016/j.jmaa.2006.02.058MathSciNetView ArticleMATHGoogle Scholar - O′Regan D, Hussain N:
**Generalized I-contractions and pointwise R-subweakly commuting maps.***Acta Math Sinica*2007,**23:**1505–1508. 10.1007/s10114-007-0935-7MathSciNetView ArticleMATHGoogle Scholar - Pathak HK, Hussain N:
**Common fixed points for Banach operator pairs with applications.***Nonlinear Anal*2008,**69:**2788–2802. 10.1016/j.na.2007.08.051MathSciNetView ArticleMATHGoogle Scholar - Ciric LB:
**A generalization of Banachs contraction principle.***Proc Am Math Soc*1974,**45:**267–273.MathSciNetView ArticleMATHGoogle Scholar - Pathak HK, Hussain N:
**Common fixed points for**$\mathcal{P}$**-operator pair with applications.***Appl Math Comput*2010,**217:**3137–3143. 10.1016/j.amc.2010.08.046MathSciNetView ArticleMATHGoogle Scholar - Hussain N, Khamsi MA, Latif A:
**Common fixed points for**$\mathcal{J}\mathcal{H}$**-operators and occasionally weakly biased pairs under relaxed conditions.***Nonlinear Anal*2011,**74**(6):2133–2140. 10.1016/j.na.2010.11.019MathSciNetView ArticleMATHGoogle Scholar - Jungck G:
**Common fixed points for commuting and compatible maps on compacta.***Proc Am Math Soc*1988,**103:**977–983. 10.1090/S0002-9939-1988-0947693-2MathSciNetView ArticleMATHGoogle Scholar - Jungck G, Rhoades BE:
**Fixed points for set valued functions without continuity.***Indian J Pure Appl Math*1998,**29:**227–238.MathSciNetMATHGoogle Scholar - Jungck G, Rhoades BE:
**Fixed point theorems for occasionally weakly compatible mappings.***Fixed Point Theory*2006,**7:**287–296.MathSciNetMATHGoogle Scholar - Chen J, Li Z:
**Common fixed points for Banach operator pairs in best approximation.***J Math Anal Appl*2007,**336:**1466–1475. 10.1016/j.jmaa.2007.01.064MathSciNetView ArticleMATHGoogle Scholar - Shahzad N:
**A result on best approximation.***Tamkang J Math*1998,**29:**223–226. corrections: Tamkang J Math**30**, 165 (1999)MathSciNetMATHGoogle Scholar - Singh SP, Watson B, Srivastava P:
*Fixed Point Theory and Best Approximation: The KKM-map Principle.*Kluwer Academic Publishers, Dordrecht; 1997.View ArticleGoogle Scholar

## Copyright

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.