# Some nano topological structures via ideals and graphs

## Abstract

In this paper, new forms of nano continuous functions in terms of the notion of nano -open sets called nano -continuous functions, strongly nano -continuous functions and nano -irresolute functions will be introduced and studied. We establish new types of nano -open functions, nano -closed functions and nano -homeomorphisms. A comparison between these types of functions and other forms of continuity will be discussed. We prove the isomorphism between simple graphs via the nano continuity between them. Finally, we apply these topological results on some models for medicine and physics which will be used to give a solution for some real-life problems.

## Introduction and preliminaries

The theory of nano topology was introduced by Lellis Thivagar et al. . They defined a nano topological space with respect to a subset X of a universe U which is defined based on lower and upper approximations of X.

Definition 1.1 . Let U be a certain set called the universe set and let R be an equivalence relation on U. The pair (U, R) is called an approximation space. Elements belonging to the same equivalence class are said to be indiscernible with one another. Let XU.

1. (i)

The lower approximation of X with respect to R is the set of all objects, which can be for certain classified as X with respect to R and it is denoted by LR(X). That is $${L}_R(X)=\bigcup \limits_{x\in U}\left\{{R}_x:{R}_x\subseteq X\right\}$$, where Rx denotes to the equivalence class determined by x.

2. (ii)

The upper approximation of X with respect to R is the set of all objects, which can be possibly classified as X with respect to R and it is denoted by UR(X) . That is $${U}_R(X)=\bigcup \limits_{x\in U}\left\{{R}_x:{R}_x\cap X\ne \varnothing \right\}$$, where Rx denotes to the equivalence class determined by x.

3. (iii)

The boundary region of X with respect to R is the set of all objects, which can be classified neither as X nor as not X with respect to R and it is denoted by BR(X). That is BR(X) = UR(X) − LR(X), where Rx denotes the equivalence class determined by x.

According to Pawlak’s definition, X is called a rough set if UR(X) ≠ LR(X).

Definition 1.2 [3, 4]. Let U be the universe and R be an equivalence relation on U and τR(X) = {U,   , LR(X), UR(X), BR(X)}, where XU and τR(X ) satisfies the following axioms:

1. (i)
$$U\ and\varnothing \in {\tau}_R(X);$$
2. (ii)

The union of elements of any sub-collection of τR(X) is in τR(X);

3. (iii)

The intersection of the elements of any finite sub-collection of τR(X) in τR(X).

That is τR(X) forms a topology on U. (U, τR(X)) is called a nano topological space. Nano-open sets are the elements of (U, τR(X)). It originates from the Greek word ‘nanos’ which means ‘dwarf’ in its modern scientific sense, an order to magnitude-one billionth. The topology is named as nano topology so because of its size since it has at most five elements . The dual nano topology is [τR(X)]c = FR(X) and its elements are called nano closed sets.

Lellis Thivagar et al.  defined the concept of nano topological space via a direct simple graph.

Definition 1.3 [5, 6]. A graph G is an ordered pair of disjoint sets (V, E), where V is non-empty and E is a subset of unordered pairs of V. The vertices and edges of a graph G are the elements of V = V(G) and E = E(G), respectively. We say that a graph G is finite (resp. infinite) if the set V(G) is finite (resp. finite).

Definition 1.4 . Let G(V, E) be a directed graph and u, vV(G), then:

1. (i)

u is invertex of v if $$\overrightarrow{uv}\in E(G)$$.

2. (ii)

u is outvertex of v if $$\overrightarrow{vu}\in E(G)$$.

3. (iii)

The neighborhood of v is denoted by N(v), and given by $$N(v)=\left\{v\right\}\cup \left\{u\in V\ (G):\overrightarrow{vu}\in E(G)\right\}$$

Definition 1.5. Let G(V, E) be a graph and H be a subgraph of G. Then

1. (i)

 The lower approximation L : P(V(G)) P(V(G)) is $${L}_N\left(V(H)\right)=\bigcup \limits_{v\in V(G)}\left\{v:N(v)\subseteq V(H)\right\}$$;

2. (ii)

 The upper approximation U : P(V(G)) P(V(G)) is $${U}_N\left(V(H)\right)=\bigcup \limits_{v\in V(G)}\left\{v:N(v)\cap V(H)\ne \varnothing \right\}$$;

3. (iii)

 The boundary is BN(V(H)) = UN(V(H)) − LN(V(H)).

Let G be a graph, N(v) be a neighbourhood of v in V and H be a subgraph of G. τN(V(H)) = {V(G),  , LN(V(H)), UN(V(H)), BN(V(H))} forms a topology on V(G) called the nano topology on V(G) with respect to V(H). (V(G), τN(V(H))) is a nano topological space induced by a graph G.

Nano closure and nano interior of a set are also studied by Lellis Thivagar and Richard and put their definitions as:

Definition 1.6 . If (U, τR(X)) is a nano topological space with respect to X where XU. If AU, then the nano interior of A is defined as the union of all nano-open subsets of A and it is denoted by NInt(A). That is, NInt(A) is the largest nano-open subset of A. The nano closure of A is defined as the intersection of all nano closed sets containing A and it is denoted by NCl(A). That is, NCl(A) is the smallest nano closed set containing A.

Continuity of functions is one of the core concepts of topology. The notion of nano continuous functions was introduced by Lellis Thivagar and Richard . They derived their characterizations in terms of nano closed sets, nano closure and nano interior. They also established nano-open maps, nano closed maps and nano homeomorphisms and their representations in terms of nano closure and nano interior.

Definition 1.7 . Let (U, τR(X)) and $$\left(V,{\tau}_{\acute{R}}(Y)\right)$$ be nano topological spaces. Then a mapping $$f:\left(U,{\tau}_R(X)\right)\to \left(V,{\tau}_R(Y)\right)$$ is nano continuous on U if the inverse image of every nano-open set in V is nano-open in U.

Definition 1.8 . A function$$f:\left(U,{\tau}_{\acute{R}}(X)\right)\to \left(V,{\tau}_{\acute{R}}(Y)\right)$$ is a nano-open map if the image of every nano-open set in U is nano open in V. The mapping f is said to be a nano closed map if the image of every nano closed set in U is nano closed in V.

Definition 1.9 . A function $$f:\left(U,{\tau}_{\acute{R}}(X)\right)\to \left(V,{\tau}_{\acute{R}}(Y)\right)$$ is said to be a nano homeomorphism if

1. (i)

f is 1-1 and onto,

2. (ii)

f is nano continuous and

3. (iii)

f is nano open.

Graph isomorphism is a related task of deciding when two graphs with different specifications are structurally equivalent, that is whether they have the same pattern of connections. Nano homeomorphism between two nano topological spaces are said to be topologically equivalent. Here, we are formalizing the structural equivalence for the graphs and their corresponding nano topologies generated by them.

Definition 1.10 . Two directed graphs G and H are isomorphic if there is an isomorphism f between their underlying graphs that preserves the direction of each edge. That is, e is directed from u to v if and only if f(e) is directed from f(u) to f(v).

Definition 1.11 . Two directed graphs C and D are isomorphic if D can be obtained by relabeling the vertices of C, that is, if there is a bijection between the vertices of C and those of D, such that the arcs joining each pair of vertices in C agree in both number and direction with the arcs joining the corresponding pair of vertices in D.

The subject of ideals in topological spaces have been studied by Kuratowski  and Vaidyanathaswamy . There have been many great attempts, so far, by topologies to use the concept of ideals for maneuvering investigations of different problems of topology. In this connection, one may refer to the works in [11,12,13].

Definition 1.12 . An ideal I on a set X is a nonempty collection of subsets of X which satisfies the conditions:

1. (i)

AI and BA implies BI,

2. (ii)

AI and BI implies ABI.

3. (iii)

The concept of a set operator ()α : Ρ(X) → Ρ(X) was introduced by Nasef  in 1992, which is called an α-local function of I with respect to τ. In 2013, the notion of -open set was introduced by Abd El-Monsef et al.  and has been studied by Radwan et al. [16, 17].

Definition 1.13 .: A subset A of an ideal topological space (X, τ, I) is said to be -open if it satisfies that A  int (clα[int(A)]). The family of all Ia-open sets in ideal topological space (X, τ, I) is denoted by IαO(X).

It was made clear that each open set is -open, but the converse may not be true, in general . Radwan et al. have shown that the family of all -open sets is a supra topology. In , the method of generating nano -open sets are introduced and studied by Kozae et al.

Definition 1.14 . A subset X of a nano ideal topological space (U, τ(X), I) is said to be -open if it satisfies that ANInt(NClα[NInt(A)]). The family of all nano -open sets in nano ideal topological space (U, τ(X), I) is denoted by NIαO(U). The elements of [NIαO(U)]c are nano -closed sets in nano ideal topological space (U, τ(X), I) and denoted by NIαC(U).

Also, discussions of various properties of nano -open sets are given, such as nano -closure and nano -interior of a set.

Definition 1.15 . Let (U, τ(X), I) be a nano ideal topological space and AU. The nano -interior of A is defined as the union of all nano -open subsets of A and it is denoted by NIα-Int(A). That is, NIα-Int(A) is the largest nano -open subset of A. The nano -closure of A is defined as the intersection of all nano -closed sets containing A and it is denoted by NIα-Cl(A). That is, NIα-Cl(A) is the smallest nano -closed set containing A.

## 2 NIα-continuous functions and NIα-homeomorphims

We define some new functions in this section, say, nano -continuous, nano -open (closed), nano -homeomorphism and other functions. Also, study the relationship between these functions, one to other and between them and nano continuous function, nano-open, nano closed and nano homeomorphism functions.

### 2.1 New types of NIα-continuous functions:

Definition 2.1.1. Let $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ be a function. f is said to be

1. (i)

Nano -continuous function if $${f}^{-1}(B)\in NI\alpha O(U), for\ all\ B\in {\tau}_{\acute{R}}(Y)$$.

2. (ii)

Strongly nano -continuous function if f−1(B) τR(X), for all BNIαO(V).

3. (iii)

Nano - irresolute continuous function if f−1(B) NIαO(U)for all BNIαO(V).

Proposition 2.1.2. A function $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ is nano -continuous function if and only if one of the following is satisfied;

1. (i)
$${f}^{-1}(B)\in NI\alpha C(U), for\ all\ B\in {F}_{\acute{R}}(Y).$$
2. (ii)

The inverse image of every member of the basis $$\overset{\hbox{'}}{B}$$of $${\tau}_{\acute{R}}(Y)$$ is NIα-open set in U.

3. (iii)

NIα-cl [f−1 (B)] f−1 [NCl(B)] , for all BV.

4. (iv)

f−1 [NInt (B)] NIα-int [f−1(B)] , for all BV.

Proof:

1. (i)

Necessity: let f be nano -continuous and $$B\in {F}_{\acute{R}}(Y)$$. That is, $$\left(V-B\right)\in {\tau}_{\acute{R}}(Y)$$. Since f is nano -continuous, f−1(V − B) NIαO(U). That is, (U − f−1(B )) NIαO(U). Therefore, f−1(B ) NIαC(U). Thus, the inverse image of every nano closed set in V is NIα-closed in U, if f is nano -continuous on U. Sufficiency: let $${f}^{-1}(B)\in NI\alpha C(U), for\ all\ B\in {F}_{\acute{R}}(Y)$$. Let $$B\in {\tau}_{\acute{R}}(Y)$$, then $$\left(V-B\right)\in {F}_{\acute{R}}(Y)$$ and f−1(V − B) NIαC(U). That is, (U − f−1(B)) NIαC(U) and therefore f−1(B) NIαO(U). Thus, the inverse image of every nano-open set in V is NIα-open in U. That is, f is nano -continuous on U.

2. (ii)

Necessity: let f be nano Iα-continuous on U. Let $$B\in \overset{\hbox{'}}{B}$$. Then $$B\in {\tau}_{\acute{R}}(Y)$$. Since f is nano Iα-continuous, f−1(B) NIαO(U). That is, the inverse image of every member of $$\overset{\hbox{'}}{B}$$is NIα-open set in U. Sufficiency: let the inverse image of every member of $$\overset{\hbox{'}}{B}$$be NIα-open set in U. Let G be a nano-open set in V. Then G =   {B : BB1}, where $${B}_1\in \overset{\hbox{'}}{B}$$. Then f−1(G) = f−1 ({B : BB1}) =   {f−1(B) : BB1} , where each f−1(B) NIαO(U) and hence their union, which is f−1(G) is NIα-open in U. Thus f is nano Iα-continuous on U.

3. (iii)

Necessity: if f is nano Iα-continuous and BV, $$NCl(B)\in {F}_{\overset{\hbox{'}}{R}}(Y)$$and from (i) f−1(NCl(B)) NIαC(U). Therefore, NIα-cl(f−1(NCl(B))) = f−1(NCl (B)) . Since BNCl(B), f−1(B) f−1(NCl(B)). Therefore, NIα-cl(f−1(B)) NIα-cl(f−1(NCl(B))) = f−1(NCl(B)) . That is, NIα-cl(f−1(B)) f−1(NCl(B)). Sufficiency: let NIα-cl(f−1(B)) f−1(NCl(B)) for every BV. Let $$B\in {F}_{\acute{R}}(Y)$$, then NCl(B) = B. By assumption, NIα-cl(f−1(B)) f−1(NCl(B)) = f−1 (B). Thus, NIα-cl(f−1(B)) f−1 (B). But f−1 (B) NIα-cl(f−1(B)) . Therefore, NIα-cl(f−1(B)) = f−1(B). That is, f−1(B) is NIα-closed in U for every nano closed set B in V. Therefore, f is nano Iα-continuous on U.

4. (iv)

Necessity: let f be nano Iα-continuous and BV. Then $$NInt(B)\in {\tau}_{\acute{R}}(Y)$$. Therefore, f−1(NInt(B)) NIαO(U). That is, f−1(NInt(B)) = NIα- int (f−1(NInt(B))). Also, NInt(B) B implies that NIα-int(f−1(NInt(B))) NIα-int(f−1(B)). Therefore f−1(NInt(B)) = NIα-int(f−1(NInt(B))) NIα-int(f−1(B)). That is, f−1(NInt(B)) NIα-int(f−1(B)) . Sufficiency: let f−1(NInt(B)) NIα-int(f−1(B)) for every subset B of V. If $$B\in {\tau}_{\acute{R}}(Y)$$, B = NInt(B). Also, f−1(B) = f−1(NInt(B)), but f−1(NInt(B)) NIα-int(f−1(B)). That is, f−1(B) = f−1(NInt(B)) NIα-int(f−1(B)). Therefore, f−1(B) = NIα-int(f−1(B)). Thus, f−1(B) is NIα-open in U for every nano-open set B in V. Therefore, f is nano Iα-continuous.

Proposition 2.1.3. A function $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ is strongly nano -continuous function if and only if one of the following is satisfied;

1. (i)
$${f}^{-1}(B)\in {F}_R(X), for\ all\ B\in NI\alpha C(V).$$
2. (ii)

The inverse image of every member of the basis $$\overset{\hbox{'}}{B}$$of NIα-open set of V is nano-open set in U.

3. (iii)

NCl [f−1 (B)] f−1[NIα-cl(B)], for all BV.

4. (iv)

f−1[NIα-int(B)] NInt[f−1(B)] , for all BV.

Proof:

1. (i)

Necessity: let f be strongly nano Iα-continuous and BNIαC(V). That is, (V − B) NIαO(V), since f is strongly nano Iα-continuous, f−1(V − B) τR(X), and (U − f−1(B )) τR(X). Therefore, f−1(B ) FR(X). Thus, f−1(B) FR(X), for all BNIαC(V) , if f is strongly nano Iα-continuous on U. Sufficiency: let f−1(B) FR(X), for all BNIαC(V). Let BNIαO(V). Then (V − B) NIαC(V). Then, f−1(V − B) FR(X) that is, (U − f−1(B)) FR(X). Therefore, f−1(B) τR(X). Thus, the inverse image of every NIα-open set in V is nano-open in U. That is, f is strongly nano Iα-continuous on U.

2. (ii)

Necessity: let f be strongly nano Iα-continuous on U. Let $$B\in \overset{\hbox{'}}{B}$$. Then BNIαO(V). Since f is strongly nano Iα-continuous, f−1(B) NIαO(U). That is, the inverse image of every member of $$\overset{\hbox{'}}{B}$$is nano-open set in U. Sufficiency: let the inverse image of every member of $$\overset{\hbox{'}}{B}$$be nano-open set in U. Let G be NIα-open set in V. Then G =   {B : BB1}, where $${B}_1\in \overset{\hbox{'}}{B}$$. Then f−1(G) = f−1 ({B : BB1}) =   {f−1(B) : BB1}, where each f−1(B) τR(X) and hence their union, which is f−1(G) is nano-open in U. Thus f is strongly nano Iα-continuous on U.

3. (iii)

Necessity: if f is strongly nano Iα-continuous and BV , NIα-cl(B) NIαC(V) and from (i) f−1(NIα-cl(B)) FR(X). Therefore, NCl(f−1(NIα- cl(B))) = f−1(NIα- cl(B)). Since BNIα-cl(B) , f−1(B) f−1(NIα- cl(B)). Therefore, NCl(f−1(B)) NCl(f−1(NIα- cl(B))) = (f−1(NIα-cl(B))). That is, NCl(f−1(B))  (f−1(NIα- cl(B))). Sufficiency: let NCl(f−1(B))  (f−1(NIα- cl(B))) for every BV. Let BNIαC(V). Then NIα-cl (B) = B . By assumption, NCl(f−1(B))  (f−1(NIα- cl(B))) = f−1 (B). Thus, NCl(f−1(B)) f−1(B). But f−1(B) NCl(f−1(B)). Therefore, NCl(f−1(B)) = f−1(B) . That is, f−1(B) FR(X) for every NIα-closed set B in V. Therefore, f is strongly nano Iα-continuous on U.

4. (iv)

Necessity: let f be strongly nano Iα-continuous and BV. Then NIα-int(B) NIαO(V). Therefore, (f−1(NIα-int(B))) τR(X). That is, f−1(NIα-int(B)) = NInt(f−1(NIα-int(B))) . Also, NIα-int(B) B implies that NInt(f−1(NIα-int(B))) NInt(f−1(B)). Therefore f−1(NIα-int(B)) = NInt(f−1(NIα- int (B))) NInt(f−1(B)) . That is, f−1(NIα- int(B))) NInt(f−1(B)). Sufficiency: let f−1(NIα-int(B))) NInt(f−1(B)) for every subset B of V. If B is NIα-open set in V, B = (NIα-int(B)). Also,f−1(B) = f−1(NIα-int(B)), but f−1(NIα-int(B)) NInt(f−1(B)). That is, f−1(B) = f−1(NIα-int(B)) NInt(f−1(B)). Therefore, f−1(B) = NInt(f−1(B)). Thus, f−1(B) is nano-open in U for every NIα-open set B in V. Therefore, f is strongly nano Iα-continuous.

Proposition 2.1.4. A function $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ is nano -irresolute continuous function if and only if one of the following is satisfied;

1. (i)
$${f}^{-1}(B)\in NI\alpha C(U), for\ all\ B\in NI\alpha C(V).$$
2. (ii)

The inverse image of every member of the basis $$\overset{\hbox{'}}{B}$$of NIα-open set of V is NIα-open set in U.

3. (iii)

NIα-cl [f−1 (B)] f−1[NIα-cl(B)], for all BV.

4. (iv)

f−1[NIα-int(B)] NIα-int [f−1(B)], for all BV.

Proof:

1. (i)

Necessity: let f be nano -irresolute continuous and BNIαC(V). That is, (V − B) NIαO(V). Since f is nano -irresolute continuous, f−1(V − B) NIαO(U). That is, (U − f−1(B)) NIαO(U), and therefore f−1(B ) NIαC(U). Thus, f−1(B) NIαC(U), for all BNIαC(V), if f is nano -irresolute continuous on U. Sufficiency: let f−1(B) NIαC(U), for all BNIαC(V). Let BNIαO(V). Then (V − B) is IαC(V). Then, f−1(V − B) IαC(U), that is, (U − f−1(B)) IαC(U). Therefore, f−1(B) NIαO(U). Thus, f−1(B) NIαO(U), for all BNIαO(V). That is, f is nano -irresolute continuous on U.

2. (ii)

Necessity: let f be nano Iα-irresolute continuous on U. Let $$B\in \overset{\hbox{'}}{B}$$. Then BNIαO(V). Since f is nano Iα-irresolute continuous, f−1(B) NIαO(U). That is, the inverse image of every member of $$\overset{\hbox{'}}{B}$$is NIαO(U). Sufficiency: let the inverse image of every member of $$\overset{\hbox{'}}{B}$$be NIα-open set in U. Let GNIαO(V). Then G =   {B : BB1} , where $${B}_1\in \overset{\hbox{'}}{B}$$. Then f−1(G) = f−1 ({B : BB1}) =   {f−1(B) : BB1} , where each f−1(B) NIαO(U) and hence their union, which is f−1(G). Thus f is nano Iα-irresolute continuous on U.

3. (iii)

Necessity: if f is nano Iα-irresolute continuous and BV , NIα-cl(B) NIαC(V) and from (i) f−1(NIα-cl(B)) NIαC(U). Therefore, NIα-cl(f−1(NIα- cl(B))) = f−1(NIα-cl(B)). Since BNIα-cl(B) , f−1(B) f−1(NIα-cl(B)). Therefore, NIα-cl(f−1(B)) NIα-cl(f−1(NIα-cl(B))) = (f−1(NIα-cl(B))). That is, NIα-cl(f−1(B))  (f−1(NIα-cl(B))). Sufficiency: let NIα-cl(f−1(B))  (f−1(NIα-cl(B))) for every BV. Let BNIαC(V). Then NIα-cl (B) = B . By assumption, NIα-cl(f−1(B))  (f−1(NIα-cl(B))) = f−1 (B). Thus, NIα-cl(f−1(B)) f−1 (B). But f−1 (B) NIα-cl(f−1(B)) . Therefore, NIα-cl(f−1(B)) = f−1(B) . That is, f−1(B) is NIα-closed in U for every NIα-closed set B in V. Therefore, f is nano Iα-irresolute continuous on U.

4. (iv)

Necessity: let f be nano Iα-irresolute continuous and BV. Then NIα-int(B) NIαO(V). Therefore, (f−1(NIα-int(B))) NIαO(U). That is, NIα-intf−1(NIα-int(B))) = (f−1(NIα-int(B))) . Also, NIα-int(B) B implies that NIα-int(f−1(NIα-int(B))) NIα-int(f−1(B)). Therefore f−1(NIα-int(B)) = NIα-int(f−1(NIα-int(B))) NIα-int(f−1(B)) . That is, f−1(NIα-int(B))) NIα-int(f−1(B)). Sufficiency: let f−1(NIα-int(B))) NIα-int(f−1(B)) for every subset B of V. If BNIαO(V), B = (NIα-int(B)). Also, f−1(B) = f−1(NIα-int(B)) but, f−1(Iα-int(B)) NIα-int(f−1(B)). That is, f−1(B) = f−1(NIα-int(B)) NIα-int(f−1(B)). Therefore, f−1(B) = NIα-int(f−1(B)). Thus, f−1(B) is NIα-open in U for every NIα-open set B in V . Therefore, f is nano NIα-irresolute continuous.

Remark 2.1.5. The following implication shows the relationships between different types of nano continuous functions.

The converse of the above diagram is not reversible, in general, as shown in Example 2.1.6.

Example 2.1.6. Consider the nano ideal topological spaces ( U, τR(X), I) and $$\left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that $$U=\left\{x,y,z\right\},V=\left\{a,b,c\right\},U/R=\left\{\left\{x\right\},\left\{y\right\},\left\{z\right\}\right\},V/\acute{R}=\left\{\left\{a\right\},\left\{b\right\},\left\{c\right\}\right\}$$, if we take X = {x}, Y = {b}, then $${\tau}_R(X)=\left\{U,\varnothing, \left\{x\right\}\right\},{\tau}_{\acute{R}}(Y)=\left\{V,\varnothing, \left\{b\right\}\right\}$$ and by taking I = {, {y}}, J = {, {a}, {c}, {a, c}}, so NIαO(U) = {U,   , {x}, {x, y}, {x, z}}, NIαO(V) = {V,   , {b}, {a, b}, {b, c}}. Define the function $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that

1. (i)

f(x) = f(y) = a, f(z) = c. This function is nano -continuous and nano continuous, but it is not nano -irresolute continuous for {b, c} NIαO(V), but f−1({b, c}) = {z} NIαO(U) . It is not strongly nano -continuous since {a, b} NIαO(V), but f−1({a, b}) = {x, y} τR(X).

2. (ii)

f(x) = f(z) = b and f(y) = a. This function is nano -irresolute continuous and nano -continuous but neither strongly nano -continuous nor nano continuous function for $$\left\{b\right\}\in {\tau}_{\acute{R}}(Y)\subseteq NI\alpha O(V)$$, but f−1({b}) = {x, z} τR(X).

Remark 2.1.7. Consider the function $$:\left(U,{\tau}_R(X),I\right)\to \left(V,{\tau}_{\acute{R}}(Y),J\right)$$ . The following statements are held.

1. (i)

If f is nano -continuous function, it is not necessary that the f(A) NIαC(V), for all $$A\in {F}_{\acute{R}}(Y)$$.

2. (ii)

If f is strongly nano -continuous function, it is not necessary that$$f(A)\in {\tau}_{\acute{R}}(Y)$$, for all ANIαC(U).

3. (iii)

If f is nano -irresolute continuous function, it is not necessary that f(A) NIαC(V), for all ANIαC(U).

We show this remark by using the following example.

Example 2.1.8. Consider the nano ideal topological spaces ( U, τR(X), I) and $$\left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that $$U=\left\{x,y,z\right\},V=\left\{a,b,c\right\},U/R=\left\{\left\{x\right\},\left\{y\right\},\left\{z\right\}\right\},V/\acute {R}=\left\{\left\{a\right\},\left\{b\right\},\left\{c\right\}\right\}$$, if we take X = {x}, Y = {b}, then $${\tau}_R(X)=\left\{U,\varnothing, \left\{x\right\}\right\},{\tau}_{\acute{R}}(Y)=\left\{V,\varnothing, \left\{b\right\}\right\}$$ and by taking I = {, {y}}, J = {, {a}, {c}, {a, c}}, so NIαO(U) = {U,   , {x}, {x, y}, {x, z}}, NIαO(V) = {V,   , {b}, {a, b}, {b, c}}. Define the function $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that

1. (i)

f(x) = f(y) = f(z) = c. This function is nano -continuous. But {y, z} FR(X) and f({y, z}) = {c} NIαC(V).

2. (ii)

f(x) = b and f(y) = f(z) = c. This function is strongly nano -continuous. But {y} NIαC(X) and $$f\left(\left\{y\right\}\right)=\left\{c\right\}\notin {F}_{\acute{R}}(Y)$$.

3. (iii)

f(x) = f(y) = c , f(z) = b. This function is nano -irresolute continuous. But {z} NIαC(X) and ({z}) = {b} NIαC(V) .

Definition 2.1.9. Let $$f:\left(U,{\tau}_R(X),I\right)\to \left(V,{\tau}_{\acute{R}}(Y),J\right)$$ be a function. f is said to be

1. (i)

Nano -open [nano -closed] function if f(A) NIαO(V), for all AτR(X) [f(A) NIαC(V)], for all AFR(X)) respectively.

2. (ii)

Strongly nano -open [strongly nano -closed] function if $$f(A)\in {\tau}_{\acute{R}}(Y)$$, for all ANIαO(U) [$$f(A)\in {F}_{\acute{R}}(Y)\Big]$$, for all ANIαC(U)), respectively.

3. (iii)

Nano -almost open (nano -almost closed) function if f(A) NIαO(V), for all ANIαO(U) [f(A) NIαC(V)], for all ANIαC(U)), respectively.

Remark 2.1.10. The following implication shows the relationships between different types of nano-open functions.

The converse of the above diagram is not reversible, in general, as shown in Examples 2.1.11 and 2.1.12.

Example 2.1.11. Consider the nano ideal topological spaces ( U, τR(X), I) and $$\left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that $$U=\left\{x,y,z\right\},V=\left\{a,b,c\right\},U/R=\left\{\left\{x\right\},\left\{y\right\},\left\{z\right\}\right\},V/\acute{R}=\left\{\left\{a\right\},\left\{b\right\},\left\{c\right\}\right\}$$, if we take X = {x}, Y = {b}, then $${\tau}_R(X)=\left\{U,\varnothing, \left\{x\right\}\right\},{\tau}_{\acute{R}}(Y)=\left\{V,\varnothing, \left\{b\right\}\right\}$$ and by taking I = {, {y}}, J = {, {a}, {b}, {a, b}}, so NIαO(U) = {U,   , {x}, {x, y}, {x, z}}, NIαO(V) = {V,   , {b}}. Define the function $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that f(x) = b, f(y) = a and f(z) = c. This function is nano -open and nano-open, but it is neither nano -almost open nor strongly nano -open for {x, y} NIαO(U), but f({x, y}) = {a, b} NIαO(V) and $$f\left(\left\{x,y\right\}\right)=\left\{a,b\right\}\notin {\tau}_{\acute{R}}(Y)$$.

Example 2.1.12. Consider the nano ideal topological spaces ( U, τR(X), I) and $$\left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that $$U=\left\{x,y,z\right\},V=\left\{a,b,c\right\},U/R=\left\{\left\{x\right\},\left\{y\right\},\left\{z\right\}\right\},V/\acute{R}=\left\{\left\{a\right\},\left\{b\right\},\left\{c\right\}\right\}$$, if we take X = {x}, Y = {b}, then $${\tau}_R(X)=\left\{U,\varnothing, \left\{x\right\}\right\},{\tau}_{\acute{R}}(Y)=\left\{V,\varnothing, \left\{b\right\}\right\}$$ and by taking I = {, {y}}, J = {, {a}, {c}, {a, c}}, so NIαO(U) = {U,   , {x}, {x, y}, {x, z}}, NIαO(V) = {V,   , {b}, {a, b}, {b, c}}. Define the function $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that f(x) = b, f(y) = f(z) = a. This function is nano -open and nano -almost open, but it is neither strongly nano -open nor nano-open for UτR(X) NIαO(U), but $$f(U)=\left\{a,b\right\}\notin {\tau}_{\acute{R}}(Y)$$.

Remark 2.1.13. The following implication shows the relationships between different types of nano closed functions.

The converse of the above diagram is not reversible, in general, as shown in Examples2.1.14 and 2.1.15.

Example 2.1.14. Consider the nano ideal topological spaces ( U, τR(X), I) and $$\left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that $$U=\left\{x,y,z\right\},V=\left\{a,b,c\right\},U/R=\left\{\left\{x\right\},\left\{y\right\},\left\{z\right\}\right\},V/\acute{R}=\left\{\left\{a\right\},\left\{b\right\},\left\{c\right\}\right\}$$, if we take X = {x}, Y = {b}, then $${\tau}_R(X)=\left\{U,\varnothing, \left\{x\right\}\right\},{\tau}_{\acute{R}}(Y)=\left\{V,\varnothing, \left\{b\right\}\right\}$$ and by taking I = {, {y}}, J = {, {a}, {b}, {a, b}}, so NIαO(U) = {U,   , {x}, {x, y}, {x, z}}, NIαO(V) = {V,   , {b}}. Define the function $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that f(x) = f(y) = a and f(z) = c. This function is nano -closed and nano closed, but it is neither nano -almost closed nor strongly nano -closed for {y} NIαC(U), but f({y}) = {a} NIαC(V) and $$f\left(\left\{y\right\}\right)=\left\{a\right\}\notin {F}_{\acute{R}}(Y)$$.

Example 2.1.15. Consider the nano ideal topological spaces ( U, τR(X), I) and $$\left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that $$U=\left\{x,y,z\right\},V=\left\{a,b,c\right\},U/R=\left\{\left\{x\right\},\left\{y\right\},\left\{z\right\}\right\},V/\acute{R}=\left\{\left\{a\right\},\left\{b\right\},\left\{c\right\}\right\}$$, if we take X = {x}, Y = {b}, then $${\tau}_R(X)=\left\{U,\varnothing, \left\{x\right\}\right\},{\tau}_{\acute{R}}(Y)=\left\{V,\varnothing, \left\{b\right\}\right\}$$ and by taking I = {, {y}}, J = {, {a}, {c}, {a, c}}, so NIαO(U) = {U,   , {x}, {x, y}, {x, z}}, NIαO(V) = {V,   , {b}, {a, b}, {b, c}}. Define the function $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ such that f(x) = a, f(y) = f(z) = c. This function is nano -closed and nano -almost closed, but it is neither strongly nano -closed nor nano closed for {y, z} FR(X) NIαC(U) but, $$f\left(\left\{y,z\right\}\right)=\left\{c\right\}\notin {F}_{\acute{R}}(Y)$$.

### NIα-homeomorphism functions:

Definition 2.2.1. Let $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ be a bijective function. 푓 is said to be

1. (i)

Nano -homeomorphism function if f and f−1 are both nano -continuous functions.

2. (ii)

Strongly nano -homeomorphism function if f and f−1 are both strongly nano -continuous functions.

3. (iii)

Nano -irresolute homeomorphism function if f and f−1 are both nano -irresolute continuous functions.

Remark 2.2.2. Let $$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ be a bijective function. f is said to be

1. (i)

Nano -homeomorphism function if f is both nano -continuous and nano -open function.

2. (ii)

Strongly nano -homeomorphism function if f is both strongly nano -continuous and is strongly nano -open function.

3. (iii)

Nano -irresolute homeomorphism function if f is both nano -irresolute continuous and nano -almost open function.

Proposition 2.2.3. Let$$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ and $$g:\left(\ V,{\tau}_{\acute{R}}(Y),J\right)\to \left(\ W,{\tau}_{\acute{R}}(Z),K\right)$$ be two functions. Then gf is

1. (i)

Nano continuous function if f, g are strongly nano -continuous and nano -continuous functions.

2. (ii)

Nano -continuous function if f, g are nano -irresolute continuous and nano continuous functions.

3. (iii)

Strongly nano -continuous function if f, g are strongly nano -continuous and nano -irresolute continuous functions.

Proof:

1. (i)

Take CW such that $$C\in {\tau}_{\acute{R}}(Z)$$, then g−1(C) NIαO(V) and f−1(g−1(C)) τR(X). Thus $$C\in {\tau}_{\acute{R}}(Z),{\left(g\circ f\right)}^{-1}\in {\tau}_R(X)$$, so gf is nano continuous function.

2. (ii)

Take CW such that $$C\in {\tau}_{\acute{R}}(Z)$$, then$${g}^{-1}(C)\in {\tau}_{\acute{R}}(Y)\subseteq NI\alpha O(V)$$ and f−1(g−1(C)) NIαO(U). Thus $$C\in {\tau}_{\acute{R}}(Z),{\left(g\circ f\right)}^{-1}\in NI\alpha O(U)$$, so gf is nano -continuous function.

3. (iii)

Take CW such that CNIαO(W), then g−1(C) NIαO(V) and f−1(g−1(C)) τR(X). Thus CNIαO(W), (gf)−1τR(X), and gf is strongly nano -continuous function.

Proposition 2.2.4. Let$$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ and $$g:\left(\ V,{\tau}_{\acute{R}}(Y),J\right)\to \left(\ W,{\tau}_{\acute{R}}(Z),K\right)$$ be two functions. Then gf is nano -irresolute continuous function in the following cases.

1. (i)

If f, g are both nano -irresolute continuous functions.

2. (ii)

If f, g are nano -irresolute continuous and strongly nano -continuous functions, respectively.

3. (iii)

If f, g are nano -continuous and strongly nano -continuous functions, respectively.

Proof: Take CW such that CIαO(W).

1. (i)

Since CNIαO(W) then g−1(C) NIαO(V) and f−1(g−1(C)) NIαO(U).

2. (ii)

Since CNIαO(W) then $${g}^{-1}(C)\in {\tau}_{\acute{R}}(Y)\subseteq NI\alpha O(Y)$$and f−1(g−1(C)) NIαO(U).

3. (iii)

Since CNIαO(W) then $${g}^{-1}(C)\in {\tau}_{\acute{R}}(Y)$$and f−1(g−1(C)) NIαO(U).

Thus, we have that CNIαO(W), (gf)−1NIαO(U), and gf is nano -irresolute continuous function.

Proposition 2.2.5. Let$$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ and $$g:\left(\ V,{\tau}_{\acute{R}}(Y),J\right)\to \left(\ W,{\tau}_{\acute{R}}(Z),K\right)$$ be two functions. Then gf is nano-open function in the following cases:

1. (i)

If f, g are nano -open and strongly nano -open functions, respectively.

2. (ii)

If f, g are nano-open and strongly nano -open functions, respectively.

Proof: Take AU such that AτR(X).

1. (i)

Since AτR(X) then $$f(A)\in {\tau}_{\acute{R}}(Y)\subseteq NI\alpha O(V)$$and $$g\left(f(A)\right)\in {\tau}_{\acute{R}}(Z)$$.

2. (ii)

Since AτR(X) then $$f(A)\in {\tau}_{\acute{R}}(Y)$$and $$g\left(f(A)\right)\in {\tau}_{\acute{R}}(Z)$$.

Thus, in each case, we have that $$A\in {\tau}_R(X),\left(g\circ f\right)\in {\tau}_{\acute{R}}(Z)$$, and gf is nano-open function.

Proposition 2.2.6. Let$$\kern0.5em f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ and $$g:\left(\ V,{\tau}_{\acute{R}}(Y),J\right)\to \left(\ W,{\tau}_{\acute{R}}(Z),K\right)$$ be two functions. Then gf is nano -open function in the following cases:

1. (i)

If f, g are nano -open and nano -almost open functions, respectively.

2. (ii)

If f, g are nano-open and nano -almost open functions, respectively.

3. (iii)

If f, g are nano-open and nano -open functions, respectively.

Proof: Take AU such that AτR(X).

1. (i)

Since AτR(X) then f(A) NIαO(V) and g(f(A)) NIαO(W).

2. (ii)

Since AτR(X) then $$f(A)\in {\tau}_{\acute{R}}(Y)\subseteq NI\alpha O(V)$$and g(f(A)) NIαO(W).

3. (iii)

Since AτR(X) then $$f(A)\in {\tau}_{\acute{R}}(Y)$$and g(f(A)) NIαO(W).

Thus, in each case, we have that AτR(X), (gf) NIαO(W), and gf is nano -open function.

Proposition 2.2.7. Let$$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ and $$g:\left(\ V,{\tau}_{\acute{R}}(Y),J\right)\to \left(\ W,{\tau}_{\acute{R}}(Z),K\right)$$ be two functions. Then gf is strongly nano -open function in the following cases.

1. (i)

If f, g are nano -almost open and strongly nano -open functions, respectively.

2. (ii)

If f, g are both strongly nano -open functions.

3. (iii)

If f, g are strongly nano -open and nano-open functions, respectively.

Proof: Take AU such that ANIαO(U).

1. (i)

Since ANIαO(U) then f(A) NIαO(V) and $$g\left(f(A)\right)\in {\tau}_{\acute{R}}(Z)$$.

2. (ii)

Since ANIαO(U) then $$f(A)\in {\tau}_{\acute{R}}(Y)\subseteq NI\alpha O(V)$$and $$g\left(f(A)\right)\in {\tau}_{\acute{R}}(Z)$$.

3. (iii)

Since ANIαO(U) then $$f(A)\in {\tau}_{\acute{R}}(Y)$$and $$g\left(f(A)\right)\in {\tau}_{\acute{R}}(Z)$$.

Thus, we have that $$A\in NI\alpha O(U),\left(g\circ f\right)\in {\tau}_{\acute{R}}(Z)$$, and gf is strongly nano -open function.

Proposition 2.3.6. Let$$f:\left(\ U,{\tau}_R(X),I\right)\to \left(\ V,{\tau}_{\acute{R}}(Y),J\right)$$ and $$g:\left(\ V,{\tau}_{\acute{R}}(Y),J\right)\to \left(\ W,{\tau}_{\acute{R}}(Z),K\right)$$ be two functions. Then gf is nano -almost open function in the following cases:

1. (i)

If f, g are both nano -almost open functions.

2. (ii)

If f, g are strongly nano -open and nano -almost open functions, respectively.

3. (iii)

If f, g are strongly nano -open and nano -open functions, respectively.

Proof: Take AU such that ANIαO(U).

1. (i)

Since ANIαO(U) then f(A) NIαO(V) and g(f(A)) NIαO(W).

2. (ii)

Since ANIαO(U) then $$f(A)\in {\tau}_{\acute{R}}(Y)\subseteq NI\alpha O(V)$$and g(f(A)) NIαO(W).

3. (iii)

Since ANIαO(U) then $$f(A)\in {\tau}_{\acute{R}}(Y)$$and g(f(A)) NIαO(W).

Thus, we have that ANIαO(U), (gf) NIαO(W), and gf is nano -almost open function.

## 3 Ideal expansion on topological rough sets and topological graphs

We extend both the rough sets and graphs induced by topology in Examples 3.1 and 3.2 respectively. The expansion will be used to give a decision for some diseases as flu.

Example 3.1. An example of a decision table is presented in Table 1. Four attributes [temperature, headache, nausea and cough], one decision [flu] and six cases.

Let

1. (i)

R1 = {Temperature} , the family of all equivalence classes of IND(R) is U ∕ R1 = {{1, 3, 4}, {2}, {5, 6}}

2. (ii)

R2 = {Temperature, Headache}, then U ∕ R2 = {{1, 4}, {2}, {3}, {5}, {6}}

3. (iii)

R3 = {Headache, Cough}, then U ∕ R3 = {{1, 4}, {2, 5}, {3}, {6}}.

If we take, X = {x : [x]Nausea = no} = {1, 3, 5} then

1. (i)

$${L}_{R_1}(X)=\varnothing$$, $${U}_{R_1}(X)=\left\{1,3,4,5,6\right\}$$and $${B}_{R_1}(X)=\left\{1,3,4,5,6\right\}$$. Thus $${\tau}_{R_1}(X)=\left\{U,\varnothing, \left\{1,3,4,5,6\right\}\right\}$$.

2. (ii)

$${L}_{R_2}(X)=\left\{3,5\right\}$$, $${U}_{R_2}(X)=\left\{1,3,4,5\right\}$$, and $${B}_{R_2}(X)=\left\{1,4\right\}$$. Thus $${\tau}_{R_2}(X)=\left\{X,\varnothing, \left\{1,4\right\},\left\{3,5\right\},\left\{1,3,4,5\right\}\right\}$$.

3. (iii)

$${L}_{R_3}(X)=\left\{3\right\}$$, $${U}_{R_3}(X)=\left\{1,2,3,4,5\right\}$$and $${B}_{R_3}(X)=\left\{1,2,4,5\right\}$$. Thus $${\tau}_{R_3}(X)=\left\{X,\varnothing, \left\{3\right\},\left\{1,2,4,5\right\},\left\{1,2,3,4,5\right\}\right\}$$.

If we take, I = {, {2}, {4}, {2, 4}} then

1. (i)
$${\left( NI\alpha O(U)\right)}_1=\left\{U,\varnothing, \left\{1,3,4,5,6\right\}\right\}.$$
2. (ii)
$${\left( NI\alpha O(U)\right)}_2=\left\{U,\varnothing, \left\{1,4\right\},\left\{3,5\right\},\left\{1,3,4,5\right\},\left\{1,2,3,4,5\right\},\left\{1,3,4,5,6\right\}\right\}.$$
3. (iii)
$${\left( NI\alpha O(U)\right)}_3=\left\{U,\varnothing, \left\{3\right\},\left\{1,2,4,5\right\},\left\{1,2,3,4,5\right\}\right\}.$$

Define a function$$f:\left(\ U,{\tau}_{R_3}(X),I\right)\to \left(\ V,{\tau}_{R_2}(X),I\right)$$ such that f(1) = 1, f(2) = 4, f(3) = 2, f(4) = 1, f(5) = 4 and f(6) = 6. This function is nano -continuous and nano continuous, but it is neither nano - irresolute continuous nor strongly nano -continuous for, {1, 3, 4, 5, 6}  (NIαO(U))2, but f−1({1, 3, 4, 5, 6}) = {1, 2, 4, 5, 6}  (NIαO(U))3.

Define a function$$f:\left(\ U,{\tau}_{R_2}(X),I\right)\to \left(\ V,{\tau}_{R_3}(X),I\right)$$ such that f(1) = 1, f(2) = 6, f(3) = 2, f(4) = 4, f(5) = 5 and f(6) = 2. This function is nano -continuous and nano - irresolute continuous, but it is neither nano continuous nor strongly nano -continuous for, $$\left\{1,2,4,5\right\}\in {\tau}_{R_3}(X)\subseteq {\left( NI\alpha O(U)\right)}_3$$, but $${f}^{-1}\left(\left\{1,2,4,5\right\}\right)=\left\{1,3,4,5,6\right\}\notin {\tau}_{R_2}(X)$$.

Example 3.2. A nano topology will be induced by a general graph. Figure 1 shows two different simple directed graphs G and H, where V(G) = {v1, v2, v3, v4, v5, v6} and V(H) = {w1, w2, w3, w4, w5, w6}.

From the previous figure N(v1) = {v1, v2, v4, v5}, N(v2) = {v2, v3, v6}, N(v3) = {v3, v4, v5}, N(v4) = {v4, v6}, N(v5) = {v5} and N(v6) = {v5, v6}. Let X = {v5}, then L(X) = {v5}, U(X) = {v1, v3, v5, v6} and b(X) = {v1, v3, v6}, which mean that τR = {V(G),   , {v5}, {v1, v3, v6}, {v1, v3, v5, v6} }. take I = {, {v1}} then NIαO(V(G)) = {V(G),   , {v5}, {v1, v3, v6}, {v1, v3, v5, v6}, {v1, v2, v3, v5, v6}, {v1, v3, v4, v5, v6} }.

Similarly N(w1) = {w1, w4, w5, w6}, N(w2) = {w2, w5}, N(w3) = {w3, w5, w6}, N(w4) = {w2, w3, w4},

N(w5) = {w5} and N(w6) = {w2, w6}. Let Y = {w5}, then L(Y) = {w5}, U(Y) = {w1, w2, w3, w5} and b(Y) = {w1, w2, w3}, which mean that $${\tau}_{\acute{R}}=\left\{V(H),\varnothing, \left\{{w}_5\right\},\left\{{w}_1,{w}_2,{w}_3\right\},\left\{{w}_1,{w}_2,{w}_3,{w}_5\right\}\ \right\}$$. Take J = {, {w1}} then NIαO(V(H)) = {V(H),   , {w5}, {w1, w2, w3}, {w1, w2, w3, w5}, {w1, w2, w3, w4, w5}, {w1, w2, w3, w5, w6} }.

Define a function$$f:\left(\ V(G),{\tau}_R(X),I\right)\to \left(\ V(H),{\tau}_{\acute{R}}(Y),J\right)$$ such that f(v1) = w1, f(v2) = w4, f(v3) = w3, f(v4) = w6, f(v5) = w5 and f(v6) = w6. This function is nano continuous, nano -continuous and nano – irresolute, but it is not strongly nano -continuous for, {w1, w2, w3, w4, w5} NIαO(V(H)) but f−1({w1, w2, w3, w4, w5}) = {v1, v2, v3, v5, v6} τR(X), and this function is nano open, nano -open and nano -almost open, but it is not strongly nano -open for, {v1, v3, v4, v5, v6} NIαO(V(G)), but $$f\left(\left\{{v}_1,{v}_3,{v}_4,{v}_5,{v}_6\right\}\right)=\left\{{w}_1,{w}_2,{w}_3,{w}_5,{w}_6\right\}\notin {\tau}_{\acute{R}}(Y)$$, also this function is one to one and onto, therefore it is nano homeomorphism, nano -homeomorphism and nano -irresolute homeomorphism, but it is not strongly nano -homeomorphism.

## 4 Topological models in terms of graphs and nano topology

In this section, we apply these new types of functions on some real-life problems, especially, in medicine and physics.

### 4.1 The foetal circulation

In this section, we apply some of the graphs, nano topology and NIα-open sets on some of the medical application such as the blood circulation in the foetus. [D1, D2] Foetal circulation differs from adult circulation in a variety of ways to support the unique physiologic needs of a developing foetus. Once there is adequate foetal-placental circulation established, blood transports between foetus and placenta through the umbilical cord containing two umbilical arteries and one umbilical vein. The umbilical arteries carry deoxygenated foetal blood to the placenta for replenishment, and the umbilical vein carries newly oxygenated and nutrient-rich blood back to the foetus. When delivering oxygenated blood throughout the developing foetus, there are unique physiologic needs, supported by specific structures unique to the foetus which facilitate these needs.

Through the medical application, we can mention a new topological model. From it, we can know each vertex in foetal circulation and what are the regions that send and receive the blood by dividing the foetal circulation into groups of vertices and edges and forming the graph on it (Fig. 2) . Also, we can conclude the nano topology and NIα-open sets on it. In the graph, we consider the foetal circulation as a graph G = (V, E) by working to divide it into a set of vertices and a set of edges. The vertices represent the regions where the blood flows on it. Also, the edges represent the pathway of blood through the foetal circulation (Fig. 3) . The vertices v1, v2, v3 and v4 (high oxygen content) represent placenta, umbilical vein, liver and ductus venosus respectively; the vertices v6, v7, v8, v9, v10, v14, v15, v16 and v17 (medium oxygen content) represent right atrium, right ventricle, foramen ovale, pulmonary trunk, lung, ductus arteriosus, aorta, systemic circulation and umbilical arteries respectively. Also, the vertices v5, v11, v12 and v13 (low oxygen content) represent inferior vena cava, left atrium and left ventricle respectively.

From the previous figures, we can construct the graph of the foetal circulation as shown in Fig. 4. It is easy to generate the nano topology τR on it by using the neighbourhood of each vertex.

Define a function $$f:\left(V(G),{\tau}_R\left(V(A)\right),I\right)\to \left(V(G),{\tau}_{\acute{R}}\left(V(B)\right),J\right)$$, such that f(v1) = {v6},

• $$f\left({v}_2\right)=\left\{{v}_7\right\},f\left({v}_3\right)=\left\{{v}_9\right\},f\left({v}_4\right)=\left\{{v}_{14}\right\},f\left({v}_5\right)=\left\{{v}_5\right\},f\left({v}_6\right)=\left\{{v}_1\right\},f\left({v}_7\right)=\left\{{v}_2\right\},f\left({v}_8\right)=\left\{{v}_8\right\},$$
• $$f\left({v}_9\right)=\left\{{v}_3\right\},f\left({v}_{10}\right)=\left\{{v}_{10}\right\},f\left({v}_{11}\right)=\left\{{v}_{15}\right\},f\left({v}_{12}\right)=\left\{{v}_{16}\right\},f\left({v}_{13}\right)=\left\{{v}_{13}\right\},f\left({v}_{14}\right)=\left\{{v}_4\right\},$$

f(v15) = {v11}, f(v16) = {v12} and f(v17) = {v17}. This function is nano-continuous, NIα-continuous and NIα-irresolute continuous, but it is not strongly NIα-continuous for {v1, v5, v6, v7, v8, v9, v13, v14, v15, v16, v17} NIαO(V(B)), but f−1({v1, v5, v6, v7, v8, v9, v13, v14, v15, v16, v17}) = {v1, v2, v3, v4, v5, v6, v8, v11, v12, v13, v17} τR(V(A)).

Also, this function is nano-open, NIα-open and NIα-almost open, but it is not strongly NIα-open for {v1, v2, v3, v4, v5, v6, v8, v11, v12, v13, v17} NIαO(V(A)), but $$f\left(\left\{{v}_1,{v}_2,{v}_3,{v}_4,{v}_5,{v}_6,{v}_8,{v}_{11},{v}_{12},{v}_{13},{v}_{17}\right\}\right)=\left\{{v}_1,{v}_5,{v}_6,{v}_7,{v}_8,{v}_9,{v}_{13},{v}_{14},{v}_{15},{v}_{16},{v}_{17}\right\}\notin {\tau}_{\acute{R}}\left(V(B)\right)$$.

Clearly, this function is bijective; thus, from the previous properties, f is nano-homeomorphism, NIα-homeomorphism and NIα-irresolute homeomorphism. Finally, by studying one part of this function, say A and by making new results, this function that satisfies NIα-irresolute homeomorphism makes the examination of foetal circulation simplest, and by NIα-irresolute homeomorphism that preserve all the topological properties of a given space, this new results will be used for the other part of this function, which is B. Therefore, there is no need to study all the foetal circulation.

### 4.2 Electric circuit

In this section, we study an application in physics such as an electrical circuit using graphs, nano-topology andNIα-open sets. Take two different electrical circuits and transform them into graphs that simply display different graphs. However, we can prove that these circuits have the same electrical properties with ideal nano topology on these graphs.

In Figs. 5 and 6 , there are two different electrical circuits C1 and C2 with two different graphs G1 and G2, respectively. So, by taking V(A) V(G1) and V(B) V(G2), we can construct a nano topology on them.

The neighborhood of each vertex of V(G1) : N1 = {1, 2}, N2 = {2, 5}, N3 = {1, 2, 3}, N4 = {3, 4} and N5 = {1, 4, 5}. So, by taking V(A) = {3, 4}, we get L(V(A)) = {4}, U(V(A)) = {3, 4, 5} and b(V(A)) = {3, 5} . Therefore τR(V(A)) = {V(G1),   , {4}, {3, 5}, {3, 4, 5}}. Let ={, {1}}. Then NIαO(V(A)) = {V(G1),   , {4}, {3, 5}, {3, 4, 5}, {1, 3, 4, 5}, {2, 3, 4, 5}}.

The neighbourhood of each vertex of V(G2) : Na = {a, c}, Nb = {a, b, e}, Nc = {c, d, e}, Nd = {b, d} and Ne = {d, e}. So by taking V(B) = {a, c}, we get L(V(B)) = {a}, U(V(B)) = {a, b, c} and b(V(B)) = {b, c}. Therefore $${\tau}_{\acute{R}}\left(V(B)\right)=\left\{V\left({G}_2\right),\varnothing, \left\{a\right\},\left\{b,c\right\},\left\{a,b,c\right\}\right\}$$. Let J = {, {e}}, then NIαO(V(B)) = {V(G2),   , {a}, {b, c}, {a, b, c}, {a, b, c, d}, {a, b, c, d}}.

Define a function$$f:\left(V\left({G}_1\right),{\tau}_R\left(V(A)\right),I\right)\to \left(V\left({G}_2\right),{\tau}_{\acute{R}}\left(V(B)\right),J\right)$$, such that f(1) = {e}, f(2) = {d}, f(3) = {c}, f(4) = {a} and f(5) = {b}. This function is nano-continuous, NIα-continuous and NIα-irresolute continuous, but it is not strongly NIα-continuous for {a, b, c, d} NIαO(V(B)), but f−1({a, b, c, d}) = {2, 3, 4, 5} τR(V(A)). Also, this function is nano-open, NIα-open and NIα-almost open, but it is not strongly NIα-open for {2, 3, 4, 5} NIαO(V(A)), but $$f\left(\left\{2,3,4,5\right\}\right)=\left\{a,b,c,d\right\}\notin {\tau}_{\acute{R}}\left(V(B)\right)$$. Clearly, this function is bijective and from the previous properties f is nano-homeomorphism, NIα-homeomorphism and NIα-irresolute homeomorphism. Finally, this function which satisfies the NIα-irresolute homeomorphism will make the study of the electrical circuit is easier by study one part of this function and made new results on it, then by homeomorphism, these new results can be applied to the other part of this equation.

Another application of NIα-irresolute homeomorphism is to prove that two different circuits are identical in their electrical properties. To prove that we define the previous function, $$f:\left(V\left({G}_1\right),{\tau}_R\left(V(A)\right),I\right)\to \left(V\left({G}_2\right),{\tau}_{\acute{R}}\left(V(B)\right),J\right)$$. Clearly, f is an isomorphism. Since G2 can be obtained by relabeling the vertices of G1, that is, f is a bijection between the vertices of G1 and those of G2, such that the arcs joining each pair of vertices in G1 accepted in both numbers and direction with the arcs joining the corresponding pair of vertices in G2.

We also have $$f:\left(V\left({G}_1\right),{\tau}_R\left(V(A)\right),I\right)\to \left(V\left({G}_2\right),{\tau}_{\acute{R}}\left(V(B)\right),J\right)$$ is NIα-irresolute homeomorphism for every subgraph A of G1, which will be studied in Table 2.

It is clear that from Table 2, the two circuits are NIα-irresolute homeomorphism for every subgraph A of G1, and using the previous structural equivalence technique we checked that the two circuits are equivalent.

## Conclusion

In this paper, different types of NIα-continuous, NIα-open, NIα-closed and NIα-homeomorphism are introduced and studied. Some applications on them are given in some real-life branches such as medicine and physics. We give some examples of electric circuits and study its relationship with graph theory.

## Availability of data and materials

The datasets used during the current study are available in the

The datasets generated during the current study are available from the corresponding author on reasonable request.

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## Author information

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### Contributions

Both authors jointly worked on the results and they read and approved the final manuscript.

### Corresponding author

Correspondence to Hanan Z. Hassan.

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The authors declare that they have no competing interests. 