 Original research
 Open Access
 Published:
Nano ∧_{β}sets and nano ∧_{β}continuity
Journal of the Egyptian Mathematical Society volume 28, Article number: 18 (2020)
Abstract
The concept of nano near open sets was originally proposed by Thivagar and Richard (Int. J. Math. Stat. Inven 1:3137). The main aspect of this paper is to introduce a new sort of nano near open sets namely, nano ∧_{β}sets. Fundamental properties of these sets are studied and compared to the previous one. It turns out that every nano βopen set is a nano ∧_{β}set. So, nano ∧_{β}sets are an extension of the previous nano near open sets, such as nano regular open, nano αopen, nano semiopen, nano preopen, nano γopen, and nano βopen sets. Meanwhile, it is shown that the concepts of nano ∧_{β}sets and nano δβopen sets are different and independent. Based on these new sets, nano ∧_{β}continuous functions are defined and some results involving their characterizations are derived. In addition, the concepts of nano ∨_{β}closure and nano ∧_{β}interior are presented. Their properties are used to introduce and study the nano ∧_{β}continuous functions.
54A05, 54B05, 54C05, 54C10
Introduction
Thivagar and Richard [1] established and constructed nano topological spaces, nano open sets, nano closed sets, nano interior, and nano closure. The nano αopen sets, nano semiopen sets, nano preopen sets, and nano regularopen sets are also studied in [1]. After the work of Thivagar and Richard [1] on nano near open sets, various mathematicians turned their attention to the generalizations of these sets. In this direction, the nano βopen sets and some of their properties were discussed in [2] and shown that this notion was a generalization of the other types of nano near sets [1]. More importantly, Nasef et al. [3] provided new properties of some weak forms of nano open sets and studied the relationships between them. In 2018, Hosny [4] proposed the notion of nano δβopen sets as a generalization of nano βopen sets. Consequently, it was an extension of all the previous weak forms of nano open sets in [1]. Nano continuous functions were defined in terms of nano open sets in [5]. On the other hand, nano αcontinuous, nano semicontinuous, nano precontinuous, and nano γcontinuous were investigated in [6, 7]. The concept of the nano βcontinuity was studied by Nasef et al. [3]. It was shown that this concept was an extension of the previous concepts of nano near continuous functions [5,6,7]. More recently, the notion of nano δβcontinuous functions was introduced in [4]. This notion was a generalization of nano βcontinuous. Therefore, it was a generalization of the other types of nano near continuous functions [5,6,7].
The purpose of this paper is to continue the research along these directions. The intention of the present work is to generalize the notion of nano βopen sets by proposing a study of a new structure in nano topology which is the nano ∧_{β}sets. It should be noted that the generalization of nano βopen sets by using ∧_{β}sets is very different from the generalization of nano βopen sets by using nano δβopen sets [4]. The main difference states that the family of all nano δβopen sets does not form a topology, as the intersection of two nano δβopen sets need not be a nano δβopen set as shown in [4]. While, the family of all nano ∧_{β}sets forms a topology as it is shown in this work. This new notion is not only an extension of nano βopen sets, but also can be regarded as a generalization of the other kinds of nano near open sets. This paper is organized as follows: The “Preliminaries” section contains the basic concepts of nano topological spaces. The nano ∧_{β}sets and their properties are presented in the “Nano ∧_{β}sets” section. The basic nano topological properties of this concept are also studied in this section. The relationships between the nano ∧_{β}sets and nano βopen sets are revealed through Lemma 3.2. Moreover, it is shown that the concepts of nano ∧_{β}sets and nano δβopen sets are different and independent (see Examples 3.1 and 3.2). At the end of this section, we draw a diagram to describe the relationships among nano ∧_{β}sets and the previous nano near sets. The objective of the “Nano ∧_{β}sets and lower and upper approximations” section is to obtain various forms of nano ∧_{β}sets corresponding to different cases of approximations. In the “Nano ∧_{β}continuity” section, nano ∧_{β}continuous functions are introduced as a generalization of nano βcontinuous functions. Additionally, Remark 5.2 shows that the difference between nano ∧_{β}continuous functions and nano δβcontinuous functions. The notion and the fundamental properties of nano ∨_{β}closure and nano ∧_{β}interior are given. The nano ∧_{β}continuous functions are redefined by using the concepts of nano closed sets, nano closure, nano interior, nano ∨_{β}sets (the complement of nano ∧_{β}sets), nano ∨_{β}closure and nano ∧_{β}interior. The “Conclusions” section concludes this study.
Preliminaries
Before proceeding further, let me first recall some fundamental concepts and properties in nano topological spaces.
Definition 2.1 [8] Let U be a nonempty finite set of objects called the universe and R be an equivalence relation on U. The pair (U,R) is said to be the approximation space. Let X ⊆ U:
 1.
The lower approximation of X with respect to R is denoted by L_{R}(X) = ∪_{x ∈ U}{R(x) : R(x) ⊆ X}, where R(x) denotes the equivalence class determined by x.
 2.
The upper approximation of X with respect to R is denoted by U_{R}(X) = ∪_{x ∈ U}{R(x) : R(x) ∩ X ≠ ϕ}.
 3.
The boundary region of X with respect to R is denoted by B_{R}(X) = U_{R}(X) − L_{R}(X).
Definition 2.2 [1] Let U be the universe, R be an equivalence relation on U and X ⊆ U. The nano topology on U with respect to X is defined by τ_{R}(X) = {U, ϕ, L_{R}(X), U_{R}(X), B_{R}(X)} and (U, τ_{R}(X)) is called the nano topological space. The elements of τ_{R}(X) are called nano open sets and the complement of any nano open set is called nano closed set.
Definition 2.3 [1] Let (U, τ_{R}(X)) be a nano topological space with respect to X, where X ⊆ U. For a subset A ⊆ U:
 1.
The nano interior of A is defined as the union of all nano open subsets contained in A and is denoted by nint(A).
 2.
The nano closure of A is defined as the intersection of all nano closed subsets containing A, and is denoted by ncl(A).
It should be noted that the concepts of the nano interior and the nano closure have the same topological characterizations and properties of the concepts of interior and the closure in the general topology.
Definition 2.4 [1, 2, 4] Let (U, τ_{R}(X)) be a nano topological space and A ⊆ U. The set A is said to be:
 1.
Nano regular open, if A = nint(ncl(A)).
 2.
Nano αopen, if A ⊆ nint[ncl(nint(A))].
 3.
Nano semiopen, if A ⊆ ncl(nint(A)).
 4.
Nano preopen, if A ⊆ nint(ncl(A)).
 5.
Nano γopen, if A ⊆ nint(ncl(A)) ∪ ncl(nint(A)).
 6.
Nano βopen (nano semi preopen), if A ⊆ ncl[nint(ncl(A))].
 7.
Nano δclosed, if A = ncl^{δ}(A), where ncl^{δ}(A) = {x ∈ U : A and x ∈ G}.
 8.
Nano δβopen, if A ⊆ ncl[nint(ncl^{δ}(A))].
The family of all nano regular open (respectively, nano αopen, nano semiopen, nano preopen, nano γopen, nano βopen and nano δβopen) sets in a nano topological space (U, τ_{R}(X)) is denoted by NRO(U, X) (respectively, N_{α}(U, X), NSO(U, X), NPO(U, X), N_{γ}(U, X), N_{β}(U, X)) and N_{δβ}O(U, X).
The relationships between nano near open sets are presented in Fig. 1 [4].
Definition 2.5 [1, 2, 4] A subset K of a nano topological space (U, τ_{R}(X)) is called nano regular closed (respectively, nano αclosed, nano semiclosed, nano preclosed, nano γclosed, nano βclosed, and nano δβclosed) if its complement is nano regular open (respectively, nano αopen, nano semiopen, nano preopen, nano γopen, nano βopen and nano δβopen).
Definition 2.6 Let (U, τ_{R}(X)) and \( \left(V,{\tau}_{R^{\hbox{'}}}^{\ast }(Y)\right) \) be nano topological spaces. A mapping \( f:\left(U,{\tau}_R(X)\right)\to \left(V,{\tau}_{R^{\hbox{'}}}^{\ast }(Y)\right) \) is said to be:
 1.
Nano continuous [5] if f^{−1}(B) is nano open set in U for every nano open set B in V.
 2.
Nano αcontinuous [6] if f^{−1}(B) is nano αopen set in U for every nano open set B in V.
 3.
Nano semicontinuous [6] if f^{−1}(B) is a nano semiopen set in U for every nano open set B in V.
 4.
Nano precontinuous [6] if f^{−1}(B) is a nano preopen set in U for every nano open set B in V.
 5.
Nano γcontinuous [7] if f^{−1}(B) is a nano γopen set in U for every nano open set B in V.
 6.
Nano βcontinuous [3] if f^{−1}(B) is a nano βopen set in U for every nano open set B in V.
 7.
Nano δβcontinuous [4] if f^{−1}(B) is a nano δβopen set in U for every nano open set B in V.
In the paper [4] the relationships between the different types of near nano continuous functions are studied as shown in the following diagram in Fig. 2.
Throughout this paper (U, τ_{R}(X)) is a nano topological space with respect to X where X ⊆ U, R is an equivalence relation on U, and U/R denotes the family of equivalence classes of U by R.
Nano ∧_{β}sets
This section presents a new notion in nano topology which is called nano ∧_{β}set. In addition, i indicates some nano topological properties of these sets. The results show that the proposed sets generalize the usual notions of nano near open sets [1, 2], whereas it is independent and different from nano δβopen sets [4].
Definition 3.1 Let (U, τ_{R}(X)) be a nano topological space and A naon ⊆ U.
A nano subset N − ∧_{β}(A) is defined as follows: N − ∧_{β}(A) = ∩ {G : A ⊆ G, G ∈ N_{β}(U, X)}. The complement of N − ∧_{β}(A)set is called N − ∨_{β}(A)set.
In the following lemma, I summarize the fundamental properties of the set N − ∧_{β}.
Lemma 3.1 For subsets A, B and A_{α}(α ∈ Δ) of a nano topological space (U, τ_{R}(X)), the following hold:
 1.
A ⊆ N∧_{β}(A).
 2.
If A ⊆ B, then N∧_{β}(A) ⊆ N − ∧_{β}(B).
 3.
N∧_{β}(N∧_{β}(A)) = N∧_{β}(A).
 4.
If A ∈ N_{β}(U, X)), then A = N∧_{β}(A).
 5.
N∧_{β}(∪{A_{α} : α ∈ Δ}) = ∪ {N∧_{β}(A_{α}) : α ∈ Δ}.
 6.
N∧_{β}(∩{A_{α} : α ∈ Δ}) ⊆ ∩ {N∧_{β}(A_{α}) : α ∈ Δ}.
Proof. I prove only (5) and (6) since the others are consequences of Definition 3.1.
First, for each α ∈ Δ, N∧_{β}(A_{α}) ⊆ N∧_{β}(∪_{α ∈ Δ}A_{α}). Hence, ∪_{α ∈ Δ}N∧_{β}(A_{α}) ⊆ N∧_{β}(∪_{α ∈ Δ}A_{α}). Conversely, suppose that x ∉ ∪_{α ∈ Δ}N∧_{β}(A_{α}). Then, x ∉ N∧_{β}(A_{α}) for each α ∈ Δ and hence there exists G_{α} ∈ N_{β}(U, X) such that A_{α} ⊆ G_{α} and x ∉ G_{α} for each α ∈ Δ. We have that ∪_{α ∈ Δ}A_{α} ⊆ ∪_{α ∈ Δ}G_{α} and ∪_{α ∈ Δ}G_{α} is a nano βopen set which does not contain x. Therefore, x ∉ N∧_{β}(∪_{α ∈ Δ}A_{α}). Thus, N∧_{β}(∪_{α ∈ Δ}A_{α}) ⊆ ∪_{α ∈ Δ}N∧_{β}(A_{α}).
Suppose that, x ∉ ∩ {N − ∧_{β}(A_{α}) : α ∈ Δ}. There exists α_{0} ∈ Δ such that \( x\notin N{\wedge}_{\beta}\left({A}_{\alpha_0}\right) \), and there exists a nano βopen set G such that x ∉ G and \( {A}_{\alpha_0}\subseteq G. \) We have that \( {\cap}_{\alpha \in \varDelta }{A}_{\alpha}\subseteq {A}_{\alpha_0}\subseteq G \) and x ∉ G. Therefore, x ∉ N − ∧_{β}(∩{A_{α} : α ∈ Δ}).
Remark 3.1 The inclusion in Lemma 3.1 parts 1 and 6 cannot be replaced by equality relation. Moreover, the converse of part 2 is not necessarily true as shown in the following example.
Example 3.1 Let U = {a, b, c, d} with U/R = {{a, b}, {c}, {d}} and X = {c}. Then, τ_{R}(X) = {U, ϕ, {c}}.
 i.
For part 1, if A = {a}, then N − ∧_{β}(A) = {a, c}, and N − ∧_{β}(A) ⊈ A.
 ii.
For part 6, if A = {a}, and B = {b}, then A ∩ B = ϕ, and N − ∧_{β}(A) = {a, c}, N − ∧_{β}(B) = {b, c}, N − ∧_{β}(A ∩ B) = ϕ, and N − ∧_{β}(A) ∩ N − ∧_{β}(B) = {c} ⊈ N − ∧_{β}(A ∩ B) = ϕ.
 iii.
For part 2, if A = {c}, and B = {a}, then N − ∧_{β}(A) = A, and N − ∧_{β}(B) = {a, c}. Therefore, N − ∧_{β}(A) ⊆ N − ∧_{β}(B), but A ⊈ B.
Definition 3.2 Let (U, τ_{R}(X)) be a nano topological space and A ⊆ U. A subset A is called nano ∧_{β}set if A = N − ∧_{β}(A). The complement of nano ∧_{β}set is nano ∨_{β}set. The family of all nano ∧_{β}sets and nano ∨_{β}sets are denoted by \( N{\tau}^{\wedge_{\beta }} \) and \( N{\varGamma}^{\vee_{\beta }}, \) respectively.
In Example 3.1, \( N{\tau}^{\wedge_{\beta }}=\left\{U,\phi, \left\{c\right\},\left\{a,c\right\},\left\{b,c\right\},\left\{c,d\right\},\left\{a,b,c\right\},\left\{a,c,d\right\},\left\{b,c,d\right\}\right\} \)
and \( N{\varGamma}^{\vee_{\beta }}=\left\{U,\phi, \left\{a\right\},\left\{b\right\},\left\{d\right\},\left\{a,b\right\},\left\{a,d\right\},\left\{b,d\right\},\left\{a,b,d\right\}\right\}. \)
In the following lemma, i summarize the fundamental properties of nano ∧_{β}sets which show that nano ∧_{β}sets are a generalization of nano βopen sets [2].
Lemma 3.2 For subsets A, B and A_{α}(α ∈ Δ) of a nano topological space (U, τ_{R}(X)), the following properties hold:
 1.
N − ∧_{β}(A), U, ϕ are nano ∧_{β}sets.
 2.
If A is a nanoβopen set, then A is a nano ∧_{β}set.
 3.
If A_{α} is a nano ∧_{β}set ∀α ∈ Δ, then ∪_{α ∈ Δ}A_{α} is a nano ∧_{β}set.
 4.
If A_{α} is a nano ∧_{β}set ∀α ∈ Δ, then ∩_{α ∈ Δ}A_{α} is a nano ∧_{β}set.
Proof. This follows from Lemma 3.1.
Remark 3.2 It is clear from (1), (3), and (4) in Lemma 3.2 that the family of all nano ∧_{β}sets forms a topology.
In (2) in Lemma 3.2, the converse is not necessarily true as shown in the following example.
Example 3.2 Let U = {a, b, c, d}, U/R = {{a, b},{c},{d}}, and X={a, c}. Then, τ_{R}(X) = {U, ϕ,{c},{a, b},{a, b, c}}. If A = {d}, then A is a nano ∧_{β}set, but A = {d} is not a nano βopen set.
Remark 3.3 The nano δβopen sets of Definition 2.4 [4] and the current Definition 3.2 of nano ∧_{β}sets are different and independent as shown in Fig. 3. Example 3.1 shows that {a} is a nano δβopen set, but it is not a nano ∧_{β}set. Moreover, Example 3.2 shows that {d} is a nano ∧_{β}set, but it is not a nano δβopen set.
Corollary 3.1 Let (U, τ_{R}(X)) be a nano topological space. Then,
 1.
\( \mathrm{NSO}\left(U,X\right)\cup \mathrm{NPO}\left(U,X\right)\subseteq N{\tau}^{\wedge_{\beta }}. \)
 2.
\( \mathrm{NSO}\left(U,X\right)\cap \mathrm{NPO}\left(U,X\right)\subseteq N{\tau}^{\wedge_{\beta }}. \)
Remark 3.4The equality in Corollary 3.1 does not hold in general. In Example 3.2, the set A = {d} is nano ∧_{β}set but it is neither in NSO(U, X) ∪ NPO(U, X) nor in NSO(U, X) ∩ NPO(U, X).
Proposition 3.1The intersection of a nano open and a nano ∧_{β}set is a nano ∧_{β}set.
Proof. Let A be a nano open and B be a nano ∧_{β}open. Then, A = N∧_{β}(A) and B = N∧_{β}(B).
Therefore, N − ∧_{β}(A ∩ B) ⊆ (A ∩ B), but N − ∧_{β}(A ∩ B) ⊇ (A ∩ B) from Lemma 3.1 (1).
Proposition 3.2If A and B are nano subsets of U such that A ⊆ B ⊆ ncl(nint(A)), then B is a nano ∧_{β}set in U.
Proof. It clear from Definition 2.3 [1] that,
Then,
Hence, B ⊆ ncl(nint(ncl(B))). Therefore B is nano βopen in U. Thus, by Lemma 3.2 (2) B is a nano ∧_{β}set in U.
Definition 3.3Let (U, τ_{R}(X)) be a nano topological space and A ⊆ U. The nano ∨_{β}closure of a set A, denoted by\( {\mathrm{ncl}}^{\vee_{\beta }}(A) \), is the intersection of nano ∨_{β}sets including A. The nano ∧_{β}interior of a set A, denoted by\( {\mathrm{nint}}^{\wedge_{\beta }}(A) \), is the union of nano ∧_{β}sets included in A.
The following theorem presents the main properties of nano ∨_{β}closure and nano ∧_{β}interior which are required in the sequel to study the properties of nano ∧_{β}continuous functions.
Theorem 3.1Let (U, τ_{R}(X)) be a nano topological space and A, B ⊆ U. Then, the following properties hold:
 1.
\( {\mathrm{ncl}}^{\vee_{\beta }}(A) \) is a nano ∨_{β}set and \( {\mathrm{nint}}^{\wedge_{\beta }}(A) \) is a nano ∧_{β}set.
 2.
\( {\mathrm{nint}}^{\wedge_{\beta }}(A)\subseteq A\subseteq {\mathrm{ncl}}^{\vee_{\beta }}(A). \)
 3.
\( A={\mathrm{ncl}}^{\vee_{\beta }}(A) \) iff A is a nano ∨_{β}set and \( {\mathrm{nint}}^{\wedge_{\beta }}(A)=A \) iff A is a nano ∧_{β}set.
 4.
If \( A\subseteq B,\mathrm{then}\ {\mathrm{ncl}}^{\vee_{\beta }}(A)\subseteq {\mathrm{ncl}}^{\vee_{\beta }}(B) \) and \( {\mathrm{nint}}^{\wedge_{\beta }}(A)\subseteq {\mathrm{nint}}^{\wedge_{\beta }}(B). \)
 5.
\( {\mathrm{nint}}^{\wedge_{\beta }}(A)\cup {\mathrm{nint}}^{\wedge_{\beta }}(B)\subseteq {\mathrm{nint}}^{\wedge_{\beta }}\left(A\cup B\right). \)
 6.
\( {\mathrm{ncl}}^{\vee_{\beta }}\left(A\cap B\right)\subseteq {\mathrm{ncl}}^{\vee_{\beta }}(A)\cap {\mathrm{ncl}}^{\vee_{\beta }}(B). \)
Proof. Obvious.
Remark 3.5 Example 3.1 shows that

1.
The inclusion in Theorem 3.1 parts 2, 5, and 6 can not be replaced by equality relation:
 i.
For part 2, if A = {a, b, c}, then \( {\mathrm{ncl}}^{\vee_{\beta }}(A)=U \) and so, \( {\mathrm{ncl}}^{\vee_{\beta }}(A)\nsubseteq A. \) If A = {a}, then \( {\mathrm{nint}}^{\wedge_{\beta }}(A)=\phi \) and thus, \( {\mathrm{nint}}^{\wedge_{\beta }}(A)\nsubseteq A. \)
 ii.
For part 5, if A = {a} and B = {c}, then \( A\cup B=\left\{a,c\right\},{\mathrm{nint}}^{\wedge_{\beta }}(A)=\phi, {\mathrm{nint}}^{\wedge_{\beta }}(B)=\left\{c\right\},{\mathrm{nint}}^{\wedge_{\beta }}\left(A\cup B\right)=A\cup B \) and so, \( {\mathrm{nint}}^{\wedge_{\beta }}\left(A\cup B\right)=\left\{a,c\right\}\nsubseteq \left\{c\right\}={\mathrm{nint}}^{\wedge_{\beta }}(A)\cup {\mathrm{nint}}^{\wedge_{\beta }}(B). \)
 iii.
For part 6, if A = {d} and B = {a, b, c}, then \( A\cap B=\phi, {\mathrm{ncl}}^{\vee_{\beta }}(A)=A,{\mathrm{ncl}}^{\vee_{\beta }}(B)=U,{\mathrm{ncl}}^{\wedge_{\beta }}\left(A\cap B\right)=\phi \) and so, \( {\mathrm{ncl}}^{\vee_{\beta }}(A)\cap {\mathrm{ncl}}^{\vee_{\beta }}(B)=\left\{d\right\}\nsubseteq {\mathrm{ncl}}^{\vee_{\beta }}\left(A\cap B\right)=\phi . \)
 i.

2.
The converse of part 4 is not necessarily true:
 i.
If A = {d} and B = {a, b, c}, then \( {\mathrm{ncl}}^{\vee_{\beta }}(A)=A \) and \( {\mathrm{ncl}}^{\vee_{\beta }}(B)=U \). Therefore, \( {\mathrm{ncl}}^{\vee_{\beta }}(A)\subseteq {\mathrm{ncl}}^{\vee_{\beta }}(B) \), but A ⊈ B.
 ii.
If A = {a} and B = {c}, then \( {\mathrm{nint}}^{\wedge_{\beta }}(A)=\phi \) and \( {\mathrm{nint}}^{\wedge_{\beta }}(B)=B \). Therefore, \( {\mathrm{nint}}^{\wedge_{\beta }}(A)\subseteq {\mathrm{nint}}^{\wedge_{\beta }}(B) \), but A ⊈ B.
 i.
Nano ∧_{β}sets and lower and upper approximations
The goal of this section is to investigate various forms of nano ∧_{β}sets corresponding to different cases of approximations.
Proposition 4.1If U_{R}(X) = U in a nano topological space, then N\( {\tau}^{\wedge_{\beta }} \)is P(U).
Proof. Let U_{R}(X) = U.
 1.
If L_{R}(X) = ϕ, then B_{R}(X) = U and τ_{R}(X) = {U, ϕ}. Hence, ncl(nint(ncl(A))) = U ∀ A ⊆ U, A ≠ ϕ. So A ⊆ ncl(nint(ncl(A))) ∀ A ⊆ U, A ≠ ϕ. Therefore, A is nano βopen in U. Thus, N_{β}(U, X) is P(U). Consequently, \( N{\tau}^{\wedge_{\beta }} \) is P(U).
 2.
If L_{R}(X) ≠ ϕ, then τ_{R}(X) = {U, ϕ, L_{R}(X), [L_{R}(X)]^{'}}.
 i.
If A ⊆ L_{R}(X), then ncl(nint(ncl(A))) = L_{R}(X). Therefore, A is nano βopen in U. Consequently, N\( {\tau}^{\wedge_{\beta }} \) is P(U).
 ii.
If A ⊆ [L_{R}(X)]^{'}, then ncl(nint(ncl(A))) = [L_{R}(X)]^{'}. Therefore, A is nano βopen in U. Consequently, N\( {\tau}^{\wedge_{\beta }} \) is P(U).
 iii.
If A ∩ L_{R}(X) ≠ ϕ and A ⊈ L_{R}(X), then ncl(A) = U and ncl(nint(ncl(A))) = U. Therefore, A is nano βopen in U. Thus, N_{β}(U, X) is P(U). Consequently, N\( {\tau}^{\wedge_{\beta }} \) is P(U).
 iv.
If A ∩ [L_{R}(X)]^{'} ≠ ϕ and A ⊈ [L_{R}(X)]^{'}, then ncl(A) = U and ncl(nint(ncl(A))) = U. Therefore, A is nano βopen in U. Thus, N_{β}(U, X) is P(U). Consequently, N\( {\tau}^{\wedge_{\beta }} \) is P(U).
 i.
Proposition 4.2If U_{R}(X) ≠ U in a nano topological space, then U, ϕ and any sets which intersects U_{R}(X) are nano ∧_{β}sets in U.
Proof. Let U_{R}(X) ≠ U.
 1.
If (L_{R}(X) = ϕ or L_{R}(X) = U_{R}(X)). In both cases, τ_{R}(X) = {U, ϕ, U_{R}(X)}. If A intersects U_{R}(X), then ncl(A) = U, hence ncl(nint(ncl(A))) = U. Therefore, A is a nano βopen set in U.
 2.
If L_{R}(X) ≠ ϕ, then τ_{R}(X) = {U, ϕ, L_{R}(X), U_{R}(X), B_{R}(X)}. Let A intersect U_{R}(X).
 i.
If A ∩ L_{R}(X) ≠ ϕ, then ncl(A) = [B_{R}(X)]^{'}, nint(ncl(A)) = L_{R}(X), ncl(nint(ncl(A))) = [B_{R}(X)]^{'} = [U_{R}(X)]^{'} ∪ L_{R}(X) ⊇ A. Therefore, A is nano βopen in U. Hence, it is a nano ∧_{β}set.
 ii.
If A ∩ B_{R}(X) ≠ ϕ, then ncl(A) = [L_{R}(X)]^{'}, nint(ncl(A)) = B_{R}(X),ncl(nint(ncl(A))) = [L_{R}(X)]^{'} = [U_{R}(X)]^{'} ∪ B_{R}(X) ⊇ A.Therefore, A is nano βopen in U. Hence, it is a nano ∧_{β}set.
 iii.
If A ∩ L_{R}(X) ≠ ϕ and A ∩ B_{R}(X) ≠ ϕ, then ncl(A) = U hence ncl(nint(ncl(A))) = U. Therefore, A is nano βopen in U. Hence, it is a nano ∧_{β}set.
 i.
Nano ∧_{β}continuity
The concepts of nano near continuous functions are extended to nano ∧_{β}continuous functions. It is shown that every nano βcontinuous function is nano ∧_{β}continuous function. Therefore, the nano ∧_{β}continuous functions are generalization of the other types of nano near continuous functions [3, 5,6,7].
Definition 5.1Let (U, τ_{R}(X)) and\( \left(V,{\tau}_{R^{\hbox{'}}}^{\ast }(Y)\right) \)be nano topological spaces. A mapping\( f:\left(U,{\tau}_R(X)\right)\to \left(V,{\tau}_{R^{\hbox{'}}}^{\ast }(Y)\right) \)is said to be a nano ∧_{β}continuous function if f^{−1}(B) is a nano ∧_{β}set in U for every nano open set B in V.
The relationships between nano βcontinuous and nano ∧_{β}continuous functions are given in the following remark.
Remark 5.1Every nano βcontinuous is nano ∧_{β}continuous.
The converse of Remark 5.1 is not necessarily true as shown in the following example.
Example 5.1Let U = {a, b, c, d} with U/R = {{b, c}, {a}, {d}} and X = {a, d}. Then, τ_{R}(X) = {U, ϕ, {a, d}}. Let V = {x, y, z, w} with V/R^{'} = {{z}, {w}, {x, y}}, Y = {x, w}. Then,\( {\tau}_R^{\ast }(Y)=\left\{V,\phi, \left\{w\right\},\left\{x,y\right\},\left\{x,y,w\right\}\right\}. \)
Define f : U → V as f(a) = f(d) = x, f(c) = z, f(b) = w. Then f is a nano ∧_{β}continuous, but it is not nano βcontinuous.
Remark 5.2The nano δβcontinuous of Definition 2.6 [4] and the current Definition 5.1 of nano ∧_{β}continuous are different and independent as shown inFig.4. In Example 5.1, let U/R = {{a, b}, {c}, {d}} and X = {a, c}. Then, τ_{R}(X) = {U, ϕ, {c}, {a, b}, {a, b, c}}.
Define f : U → V as f(a) = f(b) = x, f(c) = z, f(d) = w, then f is a nano ∧_{β}continuous, but it is not nano δβcontinuous. Moreover, let U/R = {{a, b}, {c}, {d}} and X = {c} in Example 5.1. Then, f is nano δβcontinuous, but it is not nano ∧_{β}continuous.
It should be noted that from Remarks 5.1 and 5.2 and Fig. 2, I present Fig. 4 which shows that the current Definition 5.1 is a generalization of Definition 2.6 in [3, 5,6,7]. Additionally, it is different and independent of Definition 2.6 [4].
Theorem 5.1Let (U, τ_{R}(X)) and\( \left(V,{\tau}_{R^{\hbox{'}}}^{\ast }(Y)\right) \)be nano topological spaces and let\( f:\left(U,{\tau}_R(X)\right)\to \left(V,{\tau}_{R^{\hbox{'}}}^{\ast }(Y)\right) \)be a mapping. Then, the following statements are equivalent:
 1.
f is nano ∧_{β}continuous.
 2.
The inverse image of every nano closed set G in V is nano ∨_{β}set in U.
 3.
\( f\left({\mathrm{ncl}}^{\vee_{\beta }}(A)\right)\subseteq \mathrm{ncl}\left(f(A)\right),\forall A\subseteq U. \)
 4.
\( {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(F)\right)\subseteq {f}^{1}\left(\mathrm{ncl}(F)\right),\forall F\subseteq V. \)
 5.
\( {f}^{1}\left(\mathrm{nint}(F)\right)\subseteq {\mathrm{nint}}^{\wedge_{\beta }}\left({f}^{1}(F)\right),\forall F\subseteq V. \)
Proof.

1.
(1) ⇒ (2); let f be nano ∧_{β}continuous and let G be a nano closed set in V. Then, V − G is nano open in V. Since, f is nano ∧_{β}continuous. Then, f^{−1}(V − G) is a nano ∧_{β}set in U. Then, f^{−1}(V − G) = U − f^{−1}(G) and hence f^{−1}(G) is nano ∨_{β}set in U.

2.
(2) ⇒ (1); let A be a nano open set in V. Then, f^{−1}(V − A) is nano ∨_{β}set in U. Then, f^{−1}(A) is nano ∧_{β}set in U. Therefore, f is nano ∧_{β}continuous.

3.
(1) ⇒ (3); let f be nano ∧_{β}continuous and let A ⊆ U. Since, f is nano ∧_{β}continuous and ncl(f(A)) is nano closed in V, f^{−1}(ncl(f(A))) is a nano ∨_{β}set in U. Since, f(A) ⊆ ncl(f(A)), f^{−1}(f(A)) ⊆ f^{−1}(ncl(f(A))), then \( {\mathrm{ncl}}^{\vee_{\beta }}(A)\subseteq {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}\left(\mathrm{ncl}\left(f(A)\right)\right)\right) \). Thus, \( {\mathrm{ncl}}^{\vee_{\beta }}(A)\subseteq {f}^{1}\left(\mathrm{ncl}\left(f(A)\right)\right) \). Therefore, \( f\left({\mathrm{ncl}}^{\vee_{\beta }}(A)\right)\subseteq \mathrm{ncl}\left(f(A)\right),\forall A\subset U. \)

4.
(3) ⇒ (1); let \( f\left({\mathrm{ncl}}^{\vee_{\beta }}(A)\right)\subseteq \mathrm{ncl}\left(f(A)\right),\forall A\subseteq U \) and let F be nano closed in V. Then, f^{−1}(F) ⊆ U. Thus, \( f\left({\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(F)\right)\right)\subseteq \mathrm{ncl}\left(f\left({f}^{1}(F)\right)\right)\subseteq \mathrm{ncl}(F)=F \) that is \( {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(F)\right)\subseteq {f}^{1}(F) \). Thus, \( {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(F)\right)\subseteq {f}^{1}(F) \), but \( {f}^{1}(F)\subseteq {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(F)\right) \). Hence, \( {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(F)\right)={f}^{1}(F) \). Therefore, f^{−1}(F) is nano ∨_{β}closed in U and hence f is nano ∧_{β}continuous.

5.
(1) ⇒ (4); let f be nano ∧_{β}continuous and let F ⊆ V. Since, F ⊆ ncl(F), then f^{−1}(F) ⊆ f^{−1}(ncl(F)) and hence \( {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(F)\right)\subseteq {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}\left(\mathrm{ncl}(F)\right)\right)={f}^{1}\left(\mathrm{ncl}(F)\right) \) as ncl(F) is nano closed in V and f is nano ∧_{β}continuous. Thus, \( {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(F)\right)\subseteq {f}^{1}\left(\mathrm{ncl}(F)\right). \)

6.
(4) ⇒ (1); let \( {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(F)\right)\subseteq {f}^{1}\left(\mathrm{ncl}(F)\right),\forall F\subseteq V \) and let G be nano closed in V. Then, \( {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(G)\right)\subseteq {f}^{1}\left(\mathrm{ncl}(G)\right)={f}^{1}(G). \) Hence, \( {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(G)\right)\subseteq {f}^{1}(G), \) but \( {f}^{1}(G)\subseteq {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(G)\right) \). Therefore, \( {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(G)\right)={f}^{1}(G) \) and hence f is nano ∧_{β}continuous.

7.
(1) ⇒ (5); let f be nano ∧_{β}continuous and let F ⊆ V. Since, nint(F) is nano open in V, then f^{−1}(nint(F)) is a nano ∧_{β}set in U. Therefore, \( {\mathrm{nint}}^{\wedge_{\beta }}\left[{f}^{1}\left(\mathrm{nint}(F)\right)\right]={f}^{1}\left(\mathrm{nint}(F)\right). \) Also, nint(F) ⊆ F implies that f^{−1}(nint(F)) ⊆ f^{−1}(F). Therefore, \( {\mathrm{nint}}^{\wedge_{\beta }}\left({f}^{1}\left(\mathrm{nint}(F)\right)\right)\subseteq {\mathrm{nint}}^{\wedge_{\beta }}\left({f}^{1}(F)\right) \). That is, \( {f}^{1}\left(\mathrm{nint}(F)\right)\subseteq {\mathrm{nint}}^{\wedge_{\beta }}\left({f}^{1}(F)\right). \)

8.
(5) ⇒ (1); let \( {f}^{1}\left(\mathrm{nint}(F)\right)\subseteq {\mathrm{nint}}^{\wedge_{\beta }}\left({f}^{1}(F)\right) \), for every subset F of V and let G be nano open in V. Then nint(G) = G. By assumption, \( {f}^{1}\left(\mathrm{nint}(G)\right)\subseteq {\mathrm{nint}}^{\wedge_{\beta }}\left({f}^{1}(G)\right) \). Thus, \( {f}^{1}(G)\subseteq {\mathrm{nint}}^{\wedge_{\beta }}\left({f}^{1}(G)\right) \). But \( {\mathrm{nint}}^{\wedge_{\beta }}\left({f}^{1}(G)\right)\subseteq {f}^{1}(G) \). Therefore, \( {f}^{1}(G)={\mathrm{nint}}^{\wedge_{\beta }}\left({f}^{1}(G)\right) \) and hence f is nano ∧_{β}continuous.
Remark 5.3 In Theorem 5.1 the equality of parts 3, 4, and 5 does not hold in general as shown in Example 5.1 that:

1.
for part 3, take A = {b}; then, \( f\left({\mathrm{ncl}}^{\vee_{\beta }}(A)\right)=\left\{w\right\}\ne \mathrm{ncl}\left(f(A)\right)=V. \)

2.
for part 4, take F = {w}; then, \( {\mathrm{ncl}}^{\vee_{\beta }}\left({f}^{1}(F)\right)=\left\{b\right\}\ne {f}^{1}\left(\mathrm{ncl}(F)\right)=U. \)

3.
for part 5, take F = {x}; then, \( {f}^{1}\left(\mathrm{nint}(F)\right)=\phi \ne {\mathrm{nint}}^{\wedge_{\beta }}\left({f}^{1}(F)\right)=\left\{a,d\right\}. \)
Conclusions
I have endeavored to generalize and extend the several weaker forms of nano open sets. In this paper, a new expansion through the nano topological structure was studied and analyzed. Some important characteristics and main properties which were related to these sets were obtained. Eventually, i depict the relationships among the weaker forms of nano open sets and nano ∧_{β}sets. The results showed that the proposed sets generalized the nano near open sets [1, 2], whereas this new notion is independent and different from nano δβopen sets [4]. The concepts of nano near continuous functions were extended to nano ∧_{β}continuous functions and the corresponding properties were examined. It was shown that the nano ∧_{β}continuous functions were a generalization of the other types of nano near continuous functions [3, 5,6,7] and they were different from nano δβcontinuous functions [4].
Availability of data and materials
Not applicable
References
Thivagar, M.L., Richard, C.: On nano forms of weakly open sets. Int. J. Math. Stat. Inven. 1(1), 31–37 (2013)
Revathy, A., Ilango, G.: On nano β open sets. Int. J. Eng. Contemp. Math. Sci. 1(2), 1–6 (2015)
Nasef, A.A., Aggour, A.I., Darwesh, S.M.: On some classes of nearly open sets in nano topological spaces. J. Egypt. Math. Soc. 24(4), 585–589 (2016)
M. Hosny, Nano δβ open sets and nano δβcontinuity. J. Egypt. Math. Soc. 26(2), 365–375 (2018)
Thivagar, M.L., Richard, C.: On nano continuity. Math. Theory Model. 7, 32–37 (2013)
Mary, D.A., Arockiarani, I.: On characterizations of nano rgbclased sets in nano topological spaces. Int. J. Mod. Eng. Res. 5(1), 68–76 (2015)
Mary, D.A., Arockiarani, I.: On bopen sets and bcontinuous functions in nano topological spaces. Int. J. Innov. Res. Stud. 3(11), 98–116 (2014)
Pawlak, Z.: Rough sets. Int. J. Comput. Inform. Sci. 11(5), 341–356 (1982)
Acknowledgements
The author sincerely thanks the anonymous reviewers for their careful reading, constructive comments, and fruitful suggestions which have helped immensely in improving the quality of the paper.
Funding
Not applicable
Author information
Affiliations
Contributions
The author of this paper is a single author. The author(s) read and approved the final manuscript.
Corresponding author
Ethics declarations
Ethics approval and consent to participate
Not applicable
Consent for publication
Not applicable
Competing interests
The author declares that she has no competing interests.
Additional information
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Hosny, M. Nano ∧_{β}sets and nano ∧_{β}continuity. J Egypt Math Soc 28, 18 (2020). https://doi.org/10.1186/s4278702000705
Received:
Accepted:
Published:
DOI: https://doi.org/10.1186/s4278702000705
Keywords
 Nano topology
 Nano ∧_{β}sets
 Nano ∧_{β}continuity