Abstract

We introduced the notions of fuzzy - functions and fuzzy completely - functions via fuzzy e-open sets. Some properties and several characterization of these types of functions are investigated.

1. Introduction

With the introduction of fuzzy sets by Zadeh [1] and fuzzy topology by Chang [2], the theory of fuzzy topological spaces was subsequently developed by several fuzzy topologist based on the concepts of general topology. In 2014, the concept of fuzzy e-open sets and fuzzy e-continuity and separations axioms and their properties were defined by Seenivasan and Kamala [3]. In this paper, we introduce the notion of fuzzy - functions, fuzzy -continuous, fuzzy completely - functions, and fuzzy e-kernel via fuzzy e-open sets and studied their properties and several characterizations of these types of functions are investigated. In this paper, we denote fuzzy e-open, fuzzy e-closed, and fuzzy regular closed as, , , and , respectively.

2. Preliminaries

Throughout this paper, and (or simply and ) represent nonempty fuzzy topological spaces on which no separation axioms are assumed, unless otherwise mentioned.

Let be any fuzzy set of . The fuzzy closure of , fuzzy interior of , fuzzy -closure of , and the fuzzy -interior of are denoted by , , , and , respectively. A fuzzy set of is called fuzzy regular open [4] (resp., fuzzy regular closed) if (resp., ).

The fuzzy -interior of fuzzy set of is the union of all fuzzy regular open sets contained in . A fuzzy set is called fuzzy -open [5] if . The complement of fuzzy -open set is called fuzzy -closed (i.e, ). A fuzzy set of is called fuzzy -preopen [6] (resp., fuzzy -semi open [7]) if (resp., ). The complement of a fuzzy -preopen set (resp., fuzzy -semiopen set) is called fuzzy -preclosed (resp., fuzzy -semiclosed).

Definition 1. A fuzzy set of a fuzzy topological space is called fuzzy e-open [3] if . Fuzzy e-closed if .
The intersection of all fuzzy e-closed sets containing is called fuzzy e-closure of and is denoted by - and the union of all fuzzy e-open sets contained in is called fuzzy e-interior of and is denoted by -

Definition 2. A mapping is said to be fuzzy [8] if the image of every fuzzy e-open set in is fuzzy e-open set in .

Definition 3. A function is called fuzzy e-irresolute [3]. is fuzzy e-open in for every fuzzy e-open set of .

Definition 4. A fuzzy set is quasicoincident [9] with a fuzzy set denoted by iff there exist such that . If and are not quasicoincident, then we write and

Definition 5. A fuzzy point is quasicoincident [9] with a fuzzy set denoted by iff there exist such that .

Definition 6. A fuzzy topological space is said to be fuzzy - [3] if for each pair of distinct points and of there exist fuzzy e-open sets and such that and and and .

Definition 7. A fuzzy topological space is said to be fuzzy - [3] if for each pair of distinct points and of there exists disjoint fuzzy e-open sets and such that and .

Definition 8. A fuzzy topological space is said to be fuzzy weakly Hausdorff [10] if each element of is an intersection of fuzzy regular closed sets.

Definition 9. A fuzzy topological space is said to be fuzzy e-normal [3] if for every two disjoint fuzzy closed sets and of there exist two disjoint fuzzy e-open sets and such that and and .

Definition 10. A fuzzy topological space is said to be fuzzy strongly normal [10] if for every two disjoint fuzzy closed sets and of there exist two disjoint fuzzy open sets and such that and .

Definition 11. A fuzzy topological space is said to be fuzzy Urysohn [11] if for every distinct points and in there exist fuzzy open sets and in such that and and

Definition 12. A space is called fuzzy S-closed [2] (resp., fuzzy e-compact [3]) if every fuzzy regular closed (resp., fuzzy e-open) cover of has a finite subcover.

Definition 13. A function is called fuzzy completely continuous [12] if is fuzzy regular open in for every fuzzy open set of .

Definition 14. A fuzzy filter base is said to be fuzzy -convergent [10] to a fuzzy point in if for any fuzzy regular closed set in containing there exists a fuzzy set such that .

Definition 15. A collection of fuzzy subsets of a fuzzy topological spaces is said to form fuzzy filterbases [13] iff for every finite collection , .

3. Fuzzy - Functions

In this section, the notion of fuzzy - functions is introduced and some characteristics and properties are studied.

Definition 16. A mapping is called fuzzy - if the inverse image of every fuzzy e-open set of is fuzzy e-closed in .

Remark 17. The concepts of fuzzy - and fuzzy e-irresolute are independent notions as illustrated in the following example.

Example 18. Let and and the fuzzy sets be defined as follows: Let and . Then, the mapping is defined by . Then, is fuzzy - but not fuzzy e-irresolute.

Example 19. Let and and the fuzzy sets are defined as follows:Let and . Then, the mapping is defined by . Then, is fuzzy e-irresolute but not fuzzy -.

Definition 20. A mapping is called fuzzy -continuous if the inverse image of every fuzzy open set of is fuzzy e-closed in .

Remark 21. Every fuzzy - function is fuzzy -continuous, but not conversely from the following example.

Example 22. Let and and the fuzzy sets are defined as follows: Let and . Then, the mapping is defined by , and . Then, is fuzzy -continuous but not fuzzy - as the fuzzy set is fuzzy e-open in but is not fuzzy e-closed set in .

Theorem 23. For a fuzzy function , if , the inverse image of for every fuzzy e-closed set of is fuzzy e-open in iff for any ; if , then -.

Proof. Let be a fuzzy e-closed set and . Then, and, by hypothesis, -. We obtain, -. Converse can be shown easily.

Theorem 24. For a fuzzy function , if , for any fuzzy e-closed set and for any , - iff there exists a fuzzy e-open set such that and .

Proof. Let be any fuzzy e-closed set and let . Then, -. Take - then -, and is fuzzy e-open in and
Conversely, let be any fuzzy e-closed set and let . By hypothesis, there exists fuzzy e-open set such that and . This implies, and then -.

Theorem 25. For a fuzzy function , the following statements are equivalent:(1)is fuzzy -.(2)For every fuzzy e- closed set in , is fuzzy e-open in .(3)For every fuzzy open set , - is fuzzy e-closed.(4)For every fuzzy closed set , - is fuzzy e-open.(5)For each and each fuzzy e-closed set in containing , there exists a fuzzy e-open set in containing such that .(6)For each and each fuzzy e-open set in noncontaining , there exists a fuzzy e-closed set in noncontaining such that .

Proof. (1) (2): let be a fuzzy e-open set in . Then, is fuzzy e-closed. By (2), is fuzzy e-open. Thus, is fuzzy e-closed. Converse can be shown easily.
(1) (3): let be a fuzzy open set. Since - is fuzzy e-open, then by (1) it follows that - is fuzzy e-closed. The converse is easy to prove.
(2) (4): let be a fuzzy closed set. Since - is fuzzy e-closed set, then by (2) it follows that - is fuzzy e-open. The converse is easy to prove.
(2) (5): let be any fuzzy e-closed set in containing . By (2), is fuzzy e-open set in and . Take . Then, . The converse can be shown easily.
(5) (6): let be any fuzzy e-open set in noncontaining . Then, is a fuzzy e-closed set containing . By (5), there exists a fuzzy e-open set in containing such that . Hence, and . Take . We obtain that is a fuzzy e-closed set in noncontaining . The converse can be shown easily.

Theorem 26. Let be a function and let be the fuzzy graph function of , defined by for every . If is fuzzy -, then is fuzzy -.

Proof. Let be a fuzzy e-closed set in ; then, is a fuzzy e-closed set in . Since is fuzzy -, then is fuzzy e-open in . Thus, is fuzzy -.

Theorem 27. Let be a family of product spaces. If a function is fuzzy -, then is fuzzy - for each where is the projection of onto .

Proof. Let be any fuzzy e-open set in . Since is a fuzzy continuous and fuzzy open set, it is a fuzzy e-open set. Now , is a fuzzy e-open in . Therefore, is a fuzzy e-irresolute function. Now , since is fuzzy -. Hence is a fuzzy e-closed set, since is a fuzzy e-open set. Hence, is fuzzy -.

Theorem 28. If the function is fuzzy -, then is fuzzy - for each .

Proof. Let be an arbitrary fixed index and let be any fuzzy e-open set of ; then, is fuzzy e-open in , where . Since is fuzzy - function, then is fuzzy e-closed in and hence is fuzzy e-closed in . This implies is fuzzy -.

Theorem 29. If is fuzzy - and is fuzzy closed set of , then is fuzzy -.

Proof. Let be a fuzzy e-open set of ; then, . Since and are fuzzy closed, hence is fuzzy e-closed in the relative topology of .

Definition 30. The intersection of all fuzzy e-open set of a fuzzy topological space containing is called the fuzzy e-kernel of (briefly, -),
The following properties hold for fuzzy sets of :(1)- iff for any fuzzy e-closed set containing .(2)- and - if is fuzzy e-open in .(3); then, --.

Theorem 31. For a fuzzy function , the following statements are equivalent:(1) is fuzzy -.(2)-- for every fuzzy set of .(3)-- for every fuzzy set of .

Proof. : let and -. There exists a fuzzy e-closed set in , such that and Therefore, . This implies that and - Thus, - and -. Hence, --.
: let ; then, . By hypothesis, ---. Hence, --.
: let be any fuzzy e-open set of ; we have --, since is fuzzy e-open and -. This implies that is fuzzy e-closed in .

Definition 32. The fuzzy e-Frontier of a fuzzy set of a fuzzy topological space is given by ---.

Theorem 33. The fuzzy point such that is not fuzzy - is exactly the union of fuzzy e-Frontier if the inverse image of the fuzzy e-closed set in contains .

Proof. Suppose that is not fuzzy - at the point ; then there exists a fuzzy e-closed set such that and for all fuzzy e-open set such that . It follows that and hence --. Thus, - and hence -.
Conversely, suppose that -, is fuzzy e-closed set of containing , and is fuzzy - at . There exists fuzzy e-open set such that and . Thus, - and hence - for each fuzzy e-closed set of containing , a contradiction. Therefore, is not fuzzy -.

Theorem 34. The following hold for functions and :(a)If is fuzzy - and is fuzzy -continuous then is fuzzy -continuous.(b)If is fuzzy - and is fuzzy e-irresolute then is fuzzy -.

Theorem 35. If is a fuzzy e-irresolute surjective function and is a fuzzy function such that is fuzzy -, then is fuzzy -.

Proof. Let be any fuzzy e-closed set in . Since is fuzzy -, is fuzzy e-open in . Therefore, is fuzzy e-open in . Since is fuzzy e-irresolute, surjection implies is fuzzy e-open in . Thus, is fuzzy -.

Theorem 36. If is a fuzzy surjective function and is a fuzzy function such that is fuzzy -continuous, then is fuzzy -continuous.

Proof. Let be any fuzzy closed set in . Since is fuzzy -continuous, is fuzzy e-open in . Therefore, is fuzzy e-open in . Since is fuzzy , surjection implies is fuzzy e-open in . Thus, is fuzzy -continuous.

4. Fuzzy Completely - Functions

In this section, the notion of fuzzy completely - functions is introduced and the relation between other functions is studied and further some structure preservation properties are investigated.

Definition 37. A mapping is called fuzzy completely - if inverse image of every fuzzy e-open set in is fuzzy regular closed in .

Example 38. Let and the fuzzy sets are defined as follows: Let and . Then, the mapping is defined by Then, is fuzzy completely -.

Remark 39. Every fuzzy completely - function is fuzzy - and fuzzy -continuous, but the converse is not true, which can be seen in the following example.

Example 40. Let and and the fuzzy sets , and are defined as follows: Let and . Then, the mapping is defined by . Then, is fuzzy -continuous and also fuzzy - but not fuzzy completely - as the fuzzy set is fuzzy e-open in but is not fuzzy regular closed set in .

From the above examples, we have the following implications.

None of the these implications is reversible.

Theorem 41. For a fuzzy function , if , the inverse image of every fuzzy e-closed set of is fuzzy -open in iff for any if , then .

Proof. Let be a fuzzy e-closed set and . Then, and, by hypothesis, . From here, . The converse can be shown easily.

Theorem 42. For a fuzzy function , if , for any fuzzy e-closed set and for any , iff there exists a fuzzy -open set such that and .

Proof. Let be any fuzzy e-closed set and let . Then, . Take ; then, ; is fuzzy -open in and
Conversely, let be any fuzzy e-closed set and let . By hypothesis, there exists fuzzy -open set such that and . This implies and then .

Theorem 43. For a fuzzy function , the following statements are equivalent:(1) is fuzzy completely -.(2)For every fuzzy e-closed set in , is fuzzy regular open in .(3)For every fuzzy open set , - is fuzzy regular closed.(4)For every fuzzy closed set , - is fuzzy regular open.(5)For each and each fuzzy e-closed set in containing , there exists a fuzzy regular open set in containing such that .(6)For each and each fuzzy e-open set in non containing , there exists a fuzzy regular closed set in noncontaining such that .

Proof. (1) (2): let be a fuzzy e-open set in . Then, is fuzzy e-closed. By (2), is fuzzy regular open. Thus, is fuzzy regular closed. Thus, is fuzzy completely -.The converse can be shown easily.
(1) (3): let be a fuzzy open set. Since - is fuzzy e-open, then by (1) it follows that - is fuzzy regular closed. The converse is easy to prove.
(2) (4): let be a fuzzy closed set. Since - is fuzzy e-closed set, then by (2) it follows that - is fuzzy regular open. The converse is easy to prove.
(2) (5): let be any fuzzy e-closed set in containing . By (2), is fuzzy regular open set in and . Take . Then, . The converse can be shown easily.
(5) (6): let be any fuzzy e-open set in noncontaining . Then, is a fuzzy e-closed set containing . By (5), there exists a fuzzy regular open set in containing such that . Hence, and . Take . We obtain that is a fuzzy regular closed set in noncontaining . The converse can be shown easily.

Theorem 44. Let be a function and let be the fuzzy graph function of , defined by for every . If is fuzzy completely -, then is fuzzy completely -.

Proof. Let be a fuzzy e-closed set in ; then, is a fuzzy e-closed set in . Since is fuzzy completely -, then is fuzzy regular open in . Thus, is fuzzy completely -.

Theorem 45. The following holds for functions and : (a)If is fuzzy - and is fuzzy completely -, then is fuzzy e-irresolute.(b)If is fuzzy completely - and is fuzzy -continuous, then is fuzzy completely continuous.

Definition 46. A fuzzy filter base is said to be fuzzy e-convergent to a fuzzy point in if for any fuzzy e-open set in containing there exists a fuzzy set such that .

Theorem 47. If a fuzzy function is fuzzy completely - for each fuzzy point and each fuzzy filter base in is fuzzy -convergent to , then the fuzzy filter base is fuzzy e-convergent to .

Proof. Let and let be any fuzzy filter base in which is fuzzy -converging to . Since is fuzzy completely -, then for any fuzzy e-open set in containing , there exists a fuzzy regular closed set in containing such that . Since is fuzzy -converging to , there exists a such that . This means that and therefore the fuzzy filter base is fuzzy e-convergent to

Theorem 48. If is a fuzzy completely - surjection and is fuzzy S-closed, then is fuzzy e-compact.

Proof. Suppose that is a fuzzy completely - surjection and is fuzzy S-closed. Let be a fuzzy e-open cover of . Since is a fuzzy completely -, then is fuzzy regular closed cover of and hence there exists finite set of such that . Therefore, we have and is fuzzy e-compact.

Theorem 49. If is a fuzzy completely - injection and is fuzzy -, then is fuzzy weakly Hausdorff.

Proof. Suppose is fuzzy -. For any distinct fuzzy points and in , there exist fuzzy e-open sets and in . Since is injective, , and . Since is fuzzy completely -, and are fuzzy regular closed sets of such that , and . This shows that is fuzzy weakly Hausdorff.

Theorem 50. If is a fuzzy completely - injection and is fuzzy e-normal, then is fuzzy strongly normal.

Proof. Let and be disjoint nonempty fuzzy closed sets of . Since is injective, and are disjoint fuzzy closed sets. Since is fuzzy e-normal, there exist fuzzy e-open sets and such that and and . This implies that - and - are fuzzy e-closed sets in . Then, since is fuzzy completely -, - and - are fuzzy regular open sets. Then, - and - and - and - are disjoint; by definition is fuzzy strongly normal.

Definition 51. A fuzzy topological space is said to be fuzzy -(- [14]) if for every fuzzy set of can be written in the form , where are fuzzy e-open (fuzzy regular open) or fuzzy e-closed (fuzzy regular closed) sets of .

Theorem 52. If is a fuzzy completely - injection and is fuzzy -, then is fuzzy -.

Proof. Let be a any fuzzy set of . Since is fuzzy -, is fuzzy e-open set of . Then, , where are fuzzy e-open set or fuzzy e-closed sets of . Since is completely - injection we have , where are fuzzy regular open sets or fuzzy regular closed sets of . Thus, is fuzzy .

Theorem 53. If is a fuzzy completely - injection and is fuzzy -, then is fuzzy Urysohn.

Proof. Let and be any two distinct fuzzy points in . Since is injective, in . Since is fuzzy -, there exist fuzzy e-open sets and in such that and and . This implies that - and - are fuzzy e-closed sets in . Then, since is fuzzy completely -, there exists fuzzy regular open sets and in containing and , respectively, such that - and -. This implies that - and -; we have that - and - are disjoint and hence ; by definition, is fuzzy Urysohn.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.