# Some Fixed-Point Theorems for Multivalued Monotone Mappings in Ordered Uniform Space

- Duran Turkoglu
^{1}Email author and - Demet Binbasioglu
^{1}

**2011**:186237

https://doi.org/10.1155/2011/186237

© D. Turkoglu and D. Binbasioglu. 2011

**Received: **22 September 2010

**Accepted: **8 March 2011

**Published: **15 March 2011

## Abstract

We use the order relation on uniform spaces defined by Altun and Imdad (2009) to prove some new fixed-point and coupled fixed-point theorems for multivalued monotone mappings in ordered uniform spaces.

## Keywords

## 1. Introduction

There exists considerable literature of fixed-point theory dealing with results on fixed or common fixed-points in uniform space (e.g., between [1–14]). But the majority of these results are proved for contractive or contractive type mapping (notice from the cited references). Also some fixed-point and coupled fixed-point theorems in partially ordered metric spaces are given in [15–20]. Recently, Aamri and El Moutawakil [2] have introduced the concept of -distance function on uniform spaces and utilize it to improve some well-known results of the existing literature involving both -contractive or -expansive mappings. Lately, Altun and Imdad [21] have introduced a partial ordering on uniform spaces utilizing -distance function and have used the same to prove a fixed-point theorem for single-valued nondecreasing mappings on ordered uniform spaces. In this paper, we use the partial ordering on uniform spaces which is defined by [21], so we prove some fixed-point theorems of multivalued monotone mappings and some coupled fixed-point theorems of multivalued mappings which are given for ordered metric spaces in [22] on ordered uniform spaces.

Now, we recall some relevant definitions and properties from the foundation of uniform spaces. We call a pair to be a uniform space which consists of a nonempty set together with an uniformity wherein the latter begins with a special kind of filter on whose all elements contain the diagonal . If and , then and are said to be -close. Also a sequence in , is said to be a Cauchy sequence with regard to uniformity if for any , there exists such that and are -close for . An uniformity defines a unique topology on for which the neighborhoods of are the sets when runs over .

A uniform space is said to be Hausdorff if and only if the intersection of all the reduces to diagonal of , that is, for implies . Notice that Hausdorffness of the topology induced by the uniformity guarantees the uniqueness of limit of a sequence in uniform spaces. An element of uniformity is said to be symmetrical if . Since each contains a symmetrical and if then and are both and -close and then one may assume that each is symmetrical. When topological concepts are mentioned in the context of a uniform space , they are naturally interpreted with respect to the topological space .

## 2. Preliminaries

We will require the following definitions and lemmas in the sequel.

Definition 2.1 (see [2]).

Let be a uniform space. A function is said to be an -distance if

for any , there exists , such that and for some imply ,

The following lemma embodies some useful properties of -distance.

Let be a Hausdorff uniform space and be an -distance on . Let and be arbitrary sequences in and , be sequences in converging to 0. Then, for , the following holds:

(a)if and for all , then . In particular, if and , then ,

(b)if and for all , then converges to ,

(c)if for all , then is a Cauchy sequence in .

Let be a uniform space equipped with -distance . A sequence in is -Cauchy if it satisfies the usual metric condition. There are several concepts of completeness in this setting.

Let be a uniform space and be an -distance on . Then

(i) said to be -complete if for every -Cauchy sequence there exists with ,

(ii) is said to be -Cauchy complete if for every -Cauchy sequence there exists with with respect to ,

(iv) is -continuous if with respect to implies with respect to .

Remark 2.4 (see [2]).

Let be a Hausdorff uniform space and let be a -Cauchy sequence. Suppose that is -complete, then there exists such that . Then Lemma 2.2(b) gives that with respect to the topology which shows that -completeness implies -Cauchy completeness.

Lemma 2.5 (see [15]).

## 3. The Fixed-Point Theorems of Multivalued Mappings

Theorem 3.1.

Let a Hausdorff uniform space and is an -distance on , be a function which is bounded below and " " the order introduced by . Let be also a -Cauchy complete space, be a multivalued mapping, and . Suppose that:

(i) is upper semicontinuous, that is, and with and , implies ,

such that . Moreover if is lower semicontinuous, then for all .

Proof.

By the condition (ii), take . From (iii), there exist and . Again from (iii), there exist . Thus .

which shows that (in view of Lemma 2.2(c)) that is -Cauchy sequence. By the -Cauchy completeness of , converges to . Since is upper semicontinuous, .

Similarly, we can prove the following.

Theorem 3.2.

Let a Hausdorff uniform space and an -distance on , be a function which is bounded above and " " the order introduced by . Let be also a -Cauchy complete space, be a multivalued mapping, and . Suppose that

(i) is upper semicontinuous, that is, and with and , implies ,

such that . Moreover, if is upper semicontinuous, then for all .

Corollary 3.3.

Let a Hausdorff uniform space and is an -distance on , be a function which is bounded below and " " the order introduced by . Let be also a -Cauchy complete space, be a multivalued mapping and . Suppose that:

(i) is upper semicontinuous, that is, and with and , implies ,

(ii) satisfies the monotonic condition: for any , with and any , there exists such that ,

(iii)there exists an such that .

such that . Moreover if is lower semicontinuous, then for all .

Proof.

By (iii), . For , take and . By the monotonicity of , there exists such that . So , and . The conclusion follows from Theorem 3.1.

Corollary 3.4.

Let a Hausdorff uniform space and is an -distance on , be a function which is bounded above and " " the order introduced by . Let be also a -Cauchy complete space, be a multivalued mapping and . Suppose that:

(ii) satisfies the monotonic condition; for any with and any , there exists such that ,

(iii)there exists an such that .

such that . Moreover if is upper semicontinuous, then for all .

Corollary 3.5.

Let a Hausdorff uniform space and is an -distance on , be a function which is bounded below and " " the order introduced by . Let be also a -Cauchy complete space, be a map and . Suppose that:

converges to . Moreover if is lower semicontinuous, then for all .

Corollary 3.6.

Let be a Hausdorff uniform space, is an -distance on , be a function which is bounded above, and " " the order introduced by . Let be also a -Cauchy complete space, be a map and . Suppose that:

converges to . Moreover, if is upper semicontinuous, then for all .

Corollary 3.7.

Let be a Hausdorff uniform space, is an -distance on , be a function which is bounded below, and " " the order introduced by . Let be also a -Cauchy complete space, be a map and . Suppose that:

(ii) is monotone increasing, that is, for we have ,

converges to . Moreover if is lower semicontinuous, then for all .

Example 3.8.

Let and . Define as for all , , ve . Since definition of , and this show that the uniform space is a Hausdorff uniform space. On the other hand, , and for and thus is an -distance as it is a metric on . Next define , , . Since , therefore . But as therefore and . Again similarly and which show that this ordering is partial and hence is a partially ordered uniform space. Define as , and , then by a routine calculation one can verify that all the conditions of Corollary 3.7 are satisfied and has a fixed-point. Notice that which shows that is neither -contractive nor expansive, therefore the results of [2] are not applicable in the context of this example. Thus, this example demonstrates the utility of our result.

Corollary 3.9.

Let be a Hausdorff uniform space, is an -distance on , be a function which is bounded above and " " the order introduced by . Let be also a -Cauchy complete space and be a map. Suppose that

(ii) is monotone increasing, that is, for we have ,

converges to . Moreover if is upper semicontinuous, then for all .

Theorem 3.10.

Let be a Hausdorff uniform space, is an -distance on , be a continuous function bounded below and " " the order introduced by . Let be also a -Cauchy complete space, be a multivalued mapping and . Suppose that

(i) satisfies the monotonic condition: for each and each there exists such that ,

Proof.

We will prove that has a maximum element. Let be a totally ordered subset in , where is a directed set. For and , one has , which implies that for . Since is bounded below, is a convergence net in . From , we get that is a -cauchy net in . By the -Cauchy completeness of , let converge to in .

For , by the condition (i), for each , there exists a such that . By the compactness of , there exists a convergence subnet of . Suppose that converges to . Take such that implies .

So and this gives that . Hence we have proven that has an upper bound in .

By Zorn's Lemma, there exists a maximum element in . By the definition of , there exists a such that . By the condition (i), there exists a such that . Hence . Since is the maximum element in , it follows that and . So is a fixed-point of .

Theorem 3.11.

Let be a Hausdorff uniform space, is an -distance on , be a continuous function bounded above and " " the order introduced by . Let be also a -Cauchy complete space, be a multivalued mapping and . Suppose that

(i) satisfies the following condition; for each and , there exists such that ,

Corollary 3.12.

Let be a Hausdorff uniform space, is an -distance on , be a continuous function bounded below and " " the order introduced by . Let be also a -Cauchy complete space and be a map. Suppose that;

(i) is monotone increasing, that is for , ,

Corollary 3.13.

Let be a Hausdorff uniform space, is an -distance on , be a continuous function bounded above and " " the order introduced by . Let be also a -Cauchy complete space and be a map. Suppose that;

## 4. The Coupled Fixed-Point Theorems of Multivalued Mappings

Definition 4.1.

An element is called a coupled fixed-point of the multivalued mapping if , .

Theorem 4.2.

Let be a Hausdorff uniform space, is an -distance on , be a function bounded below and " " be the order in introduced by . Let be also a -Cauchy complete space, be a multivalued mapping, , , and , and . Suppose that:

(i) is upper semicontinuous, that is, , and , with , and implies ,

(iii)for each , there is such that and .

Proof.

By the condition (ii), take . From (iii), there exist such that , and , . Again from (iii), there exist such that , and , .

From this we get that and are convergent sequences. By the definition of " " as in the proof of Theorem 3.1, it is easy to prove that and are -Cauchy sequences. Since is -Cauchy complete, let converge to and converge to . Since is upper semicontinuous, and . Hence is a coupled fixed-point of .

Corollary 4.3.

Let be a Hausdorff uniform space, is an -distance on , be a function bounded below, and " " be the order in introduced by . Let be also a -Cauchy complete space, be a mapping and and and . Suppose that;

Then has a coupled fixed-point , that is, and . And there exist two sequences and with , , such that and .

Corollary 4.4.

Let be a Hausdorff uniform space, is an -distance on , be a function bounded below, and " " be the order in introduced by . Let be also a -Cauchy complete space, be a mapping and and and . Suppose that;

(iii) is mixed monotone, that is for each and , .

Then has a coupled fixed-point . And there exist two sequences and with , , such that and .

Theorem 4.5.

Let be a Hausdorff uniform space, is an -distance on , be a continuous function, and " " be the order in introduced by . Let be also a -Cauchy complete space, be a multivalued mapping, , , and , and . Suppose that;

(i) is mixed monotone, that is, for , and , , there exist , such that , ,

Then has a coupled fixed-point.

Proof.

It is easy to prove that becomes an ordered space.

So and , this gives that . Hence we have proven that has an upper bound in .

By Zorn's lemma, there exists a maximum element in . By the definition of , there exist , , such that , and , . By the condition (i) there exist , such that and . Hence and . Since is maximum element in , it follows that , and it follows that and . So is a coupled fixed-point of .

Corollary 4.6.

Let be a Hausdorff uniform space, is an -distance on , be a continuous function, and " " be the order in introduced by . Let be also a -Cauchy complete space and be a mapping. Suppose that;

(i) is mixed monotone, that is for , and ,

## Authors’ Affiliations

## References

- Aamri M, Bennani S, El Moutawakil D:
**Fixed points and variational principle in uniform spaces.***Siberian Electronic Mathematical Reports*2006,**3:**137–142.MATHMathSciNetGoogle Scholar - Aamri M, El Moutawakil D:
**Common fixed point theorems for E-contractive or E-expansive maps in uniform spaces.***Acta Mathematica Academiae Peadegogicae Nyiregy-Haziensis*2004,**20**(1):83–91.MATHMathSciNetGoogle Scholar - Aamri M, El Moutawakil D:
**Weak compatibility and common fixed point theorems for A-contractive and E-expansive maps in uniform spaces.***Serdica Mathematical Journal*2005,**31**(1–2):75–86.MATHMathSciNetGoogle Scholar - Acharya SP:
**Some results on fixed points in uniform spaces.***Yokohama Mathematical Journal*1974,**22:**105–116.MATHMathSciNetGoogle Scholar - Agarwal RP, O'Regan D, Papageorgiou NS:
**Common fixed point theory for multivalued contractive maps of Reich type in uniform spaces.***Applicable Analysis*2004,**83**(1):37–47. 10.1080/00036810310001620063MATHMathSciNetView ArticleGoogle Scholar - Olatinwo MO:
**Some common fixed point theorems for selfmappings in uniform space.***Acta Mathematica Academiae Peadegogicae Nyiregyhaziensis*2007,**23**(1):47–54.MathSciNetMATHGoogle Scholar - Olatinwo MO:
**Some existence and uniqueness common fixed point theorems for selfmappings in uniform space.***Fasciculi Mathematici*2007,**38:**87–95.MATHMathSciNetGoogle Scholar - Olatinwo MO:
**On some common fixed point theorems of Aamri and El Moutawakil in uniform spaces.***Applied Mathematics E-Notes*2008,**8:**254–262.MATHMathSciNetGoogle Scholar - O'Regan D, Agarwal RP, Jiang D:
**Fixed point and homotopy results in uniform spaces.***Bulletin of the Belgian Mathematical Society. Simon Stevin*2004,**11**(2):289–296.MATHMathSciNetGoogle Scholar - Türkoglu D:
**Fixed point theorems on uniform spaces.***Indian Journal of Pure and Applied Mathematics*2003,**34**(3):453–459.MATHMathSciNetGoogle Scholar - Turkoglu D:
**Some fixed point theorems for hybrid contractions in uniform space.***Taiwanese Journal of Mathematics*2008,**12**(3):807–820.MATHMathSciNetGoogle Scholar - Turkoglu D:
**Some common fixed point theorems for weakly compatible mappings in uniform spaces.***Acta Mathematica Hungarica*2010,**128**(1–2):165–174. 10.1007/s10474-010-9177-8MATHMathSciNetView ArticleGoogle Scholar - Türkoglu D, Fisher B:
**Fixed point of multivalued mapping in uniform spaces.***Indian Academy of Sciences*2003,**113**(2):183–187. 10.1007/BF02829768MATHMathSciNetGoogle Scholar - Türkoğlu D, Rhoades BE:
**A general fixed point theorem for multi-valued mapping in uniform space.***The Rocky Mountain Journal of Mathematics*2008,**38**(2):639–647. 10.1216/RMJ-2008-38-2-639MATHMathSciNetView ArticleGoogle Scholar - Agarwal RP, El-Gebeily MA, O'Regan D:
**Generalized contractions in partially ordered metric spaces.***Applicable Analysis*2008,**87**(1):109–116. 10.1080/00036810701556151MATHMathSciNetView ArticleGoogle Scholar - Bhaskar TG, Lakshmikantham V:
**Fixed point theorems in partially ordered metric spaces and applications.***Nonlinear Analysis: Theory, Methods & Applications*2006,**65**(7):1379–1393. 10.1016/j.na.2005.10.017MATHMathSciNetView ArticleGoogle Scholar - Guo DJ, Lakshmikantham V:
**Coupled fixed points of nonlinear operators with applications.***Nonlinear Analysis: Theory, Methods & Applications*1987,**11**(5):623–632. 10.1016/0362-546X(87)90077-0MATHMathSciNetView ArticleGoogle Scholar - Lakshmikantham V, Ciric LB:
**Coupled fixed point theorems for nonlinear contractions in partially ordered metric spaces.***Nonlinear Analysis: Theory, Methods & Applications*2009,**70**(12):4341–4349. 10.1016/j.na.2008.09.020MATHMathSciNetView ArticleGoogle Scholar - Nieto JJ, Lopez RR:
**Contractive mapping theorems in partially ordered sets and applications to ordinary differential equations.***Order*2005,**22**(3):223–239. 10.1007/s11083-005-9018-5MATHMathSciNetView ArticleGoogle Scholar - Samet B:
**Coupled fixed point theorems for a generalized Meir-Keeler contraction in partially ordered metric spaces.***Nonlinear Analysis: Theory, Methods & Applications*2010,**72**(12):4508–4517. 10.1016/j.na.2010.02.026MATHMathSciNetView ArticleGoogle Scholar - Altun I, Imdad M:
**Some fixed point theorems on ordered uniform spaces.***Filomat*2009,**23**(3):15–22. 10.2298/FIL0903015AMATHView ArticleMathSciNetGoogle Scholar - Zhang X:
**Fixed point theorems of multivalued monotone mappings in ordered metric spaces.***Applied Mathematics Letters*2010,**23**(3):235–240. 10.1016/j.aml.2009.06.011MATHMathSciNetView ArticleGoogle Scholar

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