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On the number of unit solutions of cubic congruence modulo n

  • For any positive integer n, let Zn:=Z/nZ={0,,n1} be the ring of residue classes module n, and let Z×n:={xZn|gcd(x,n)=1}. In 1926, for any fixed cZn, A. Brauer studied the linear congruence x1++xmc(modn) with x1,,xmZ×n and gave a formula of its number of incongruent solutions. Recently, Taki Eldin extended A. Brauer's result to the quadratic case. In this paper, for any positive integer n, we give an explicit formula for the number of incongruent solutions of the following cubic congruence

    x31++x3m0(modn)   with x1,,xmZ×n.

    Citation: Junyong Zhao. On the number of unit solutions of cubic congruence modulo n[J]. AIMS Mathematics, 2021, 6(12): 13515-13524. doi: 10.3934/math.2021784

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  • For any positive integer n, let Zn:=Z/nZ={0,,n1} be the ring of residue classes module n, and let Z×n:={xZn|gcd(x,n)=1}. In 1926, for any fixed cZn, A. Brauer studied the linear congruence x1++xmc(modn) with x1,,xmZ×n and gave a formula of its number of incongruent solutions. Recently, Taki Eldin extended A. Brauer's result to the quadratic case. In this paper, for any positive integer n, we give an explicit formula for the number of incongruent solutions of the following cubic congruence

    x31++x3m0(modn)   with x1,,xmZ×n.



    In 1999, Molodtsov [30] founded a novel mathematical tool for dealing with uncertainties, namely soft set. One of the merits of this tool is its free from the difficulties that the other existing methods such as fuzzy set theory and probability theory. This matter makes soft set theory very popular research area all over the globe. Immediately afterwards, Maji et al. [26] in 2003, established the basis of soft operations between soft sets. Although some of these operations were considered ill-defined, they formed the starting point of constructing soft set theory. In this regard, Ali et al. [5] redefined some soft operators to make them more functional for improving several new results and they explored new soft operators such as restricted union and restricted intersection of two soft sets.

    In 2011, Shabir and Naz [32] exploited soft sets to introduce soft topological spaces. The fundamental soft topological notions such as the operators of soft closure and interior, soft subspace and soft separation axioms were investigated by them. Min [29] completed study of soft separation axioms and revised some results obtained in [32]. Soft compactness was introduced and discussed by Aygünoǧlu and Aygün [14] in 2012. Hida [23] defined another type of soft compactness depending on the belong relations. Al-shami [10] did some amendments concern some types of soft union and intersection. Then, he [11] studied new types of soft compactness. The authors of [25] presented soft maps by using two crisp maps, one of them between the sets of parameters and the second one between the universal sets. However, the authors of [36] introduced soft maps by using the concept of soft points. Some applications of different types of soft maps were the goal of some articles, see [25,27,36].

    Until 2018, the belong and non-belong relations that utilized in these studies are those given by [32]. In 2018, the authors of [20] came up new relations of belong and non-belong between an element and soft set, namely partial belong and total non-belong relations. In fact, these relations widely open the door to study and redefine many soft topological notions. This leads to obtain many fruitful properties and changes which can be seen significantly on the study of soft separation axioms as it was showed in [9,20,21]. As another path of study soft separation axioms, the authors of [16,35] studied them with respect to the distinct soft points. Recently, some applications of compactness and soft separation axioms have been investigated in [6,7,33,34].

    Das and Samanta [19] studied the concept of a soft metric based on the soft real set and soft real numbers given in [18]. Wardowski [36] tackled the fixed point in the setup of soft topological spaces. Abbas et al.[1] presented soft contraction mappings and established a soft Banach fixed point theorem in the framework of soft metric spaces. Recently, many researchers explored fixed point findings in soft metric type spaces, see, for example, [2,37]. Some interesting works regarding deferential equations were given in [17,24,28].

    One of the significant ideas that helps to prove some properties and remove some problems on soft topology is the concept of a soft point. It was first defined by Zorlutuna et al. [38] in order to study interior points of a soft set and soft neighborhood systems. Then [19] and [31] simultaneously redefined soft points to discuss soft metric spaces. In fact, the recent definition of a soft point makes similarity between many set-theoretic properties and their counterparts on soft setting. Two types of soft topologies, namely enriched soft topology and extended soft topology were studied in [14] and [31], respectively. The equivalence between these two topologies have been recently proved by Al-shami and Kočinac [12].

    We organized this paper as follows: After this introduction, we allocate Section (2) to recall some definitions and results of soft sets and soft topologies that will help us to understand this work. Section (3) introduces tt-soft αTi(i=0,1,2,3,4) and tt-soft α-regular spaces with respect to ordinary points by using total belong and total non-belong relations. The relationships between them and their main properties are discussed with the help of interesting examples. In Section (4), we explore an α-fixed soft point theorem and study some main properties. In particular, we conclude under what conditions α-fixed soft points are preserved between a soft topological space and its parametric topological spaces. Section (6) concludes the paper.

    To well understand the results obtained in this study, we shall recall some basic concepts, definitions and properties from the literature.

    Definition 2.1. [30] For a nonempty set X and a set of parameters E, a pair (G,E) is said to be a soft set over X provided that G is a map of E into the power set P(X).

    In this study, we use a symbol GE to refer a soft set instead of (G,E) and we identify it as ordered pairs GE={(e,G(e)):eE and G(e)P(X)}.

    A family of all soft sets defined over X with E is denoted by S(XE).

    Definition 2.2. [22] A soft set GE is said to be a subset of a soft set HE, denoted by GE˜HE, if G(e)H(e) for each eE.

    The soft sets GE and HE are said to be soft equal if each one of them is a subset of the other.

    Definition 2.3. [20,32] Let GE be a soft set over X and xX. We say that:

    (ⅰ) xGE, it is read: x totally belongs to GE, if xG(e) for each eE.

    (ⅱ) xGE, it is read: x does not partially belong to GE, if xG(e) for some eE.

    (ⅲ) xGE, it is read: x partially belongs to GE, if xG(e) for some eE.

    (ⅳ) x⋐̸GE, it is read: x does not totally belong to GE, if xG(e) for each eE.

    Definition 2.4. Let GE be a soft set over X and xX. We say that:

    (ⅰ) GE totally contains x if xGE.

    (ⅱ) GE does not partially contain x if xGE.

    (ⅲ) GE partially contains x if xGE.

    (ⅳ) GE does not totally contain x if x⋐̸GE.

    Definition 2.5. [5] The relative complement of a soft set GE is a soft set GcE, where Gc:E2X is a mapping defined by Gc(e)=XG(e) for all eE.

    Definition 2.6. [19,20,26,31] A soft set (G,E) over X is said to be:

    (ⅰ) a null soft set, denoted by ˜Φ, if G(e)= for each eE.

    (ⅱ) an absolute soft set, denoted by ˜X, if G(e)=X for each eE.

    (ⅲ) a soft point Pxe if there are eE and xX such that G(e)={x} and G(e)= for each eE{e}. We write that PxeGE if xG(e).

    (ⅳ) a stable soft set, denoted by ˜S, if there is a subset S of X such that G(e)=S for each eE. In particular, we denoted by xE if S={x}.

    (ⅴ) a countable (resp. finite) soft set if G(e) is countable (resp. finite) for each eE. Otherwise, it is said to be uncountable (resp. infinite).

    Definition 2.7. [5,26] Let GE and HE be two soft sets over X.

    (ⅰ) Their intersection, denoted by GE˜HE, is a soft set UE, where a mapping U:E2X is given by U(e)=G(e)H(e).

    (ⅱ) Their union, denoted by GE˜HE, is a soft set UE, where a mapping U:E2X is given by U(e)=G(e)H(e).

    Definition 2.8. [15] Let GE and HF be two soft sets over X and Y, respectively. Then the cartesian product of GE and HF, denoted by G×HE×F, is defined as (G×H)(e,f)=G(e)×H(f) for each (e,f)E×F.

    The soft union and intersection operators were generalized for any number of soft sets in a similar way.

    Definition 2.9. [25] A soft mapping between S(XA) and S(YB) is a pair (f,ϕ), denoted also by fϕ, of mappings such that f:XY, ϕ:AB. Let GA and HB be subsets of S(XA) and S(YB), respectively. Then the image of GA and pre-image of HB are defined as follows.

    (ⅰ) fϕ(GA)=(fϕ(G))B is a subset of S(YB) such fϕ(G)(b)=aϕ1(b)f(G(a)) for each bB.

    (ⅱ) f1ϕ(HB)=(f1ϕ(H))A is a subset of S(XA) such that f1ϕ(H)(a)=f1(H(ϕ(a))) for each aA.

    Definition 2.10. [38] A soft map fϕ:S(XA)S(YB) is said to be injective (resp. surjective, bijective) if ϕ and f are injective (resp. surjective, bijective).

    Definition 2.11. [32] A family τ of soft sets over X under a fixed set of parameters E is said to be a soft topology on X if it satisfies the following.

    (ⅰ) ˜X and ˜Φ are members of τ.

    (ⅱ) The intersection of a finite number of soft sets in τ is a member of τ.

    (ⅲ) The union of an arbitrary number of soft sets in τ is a member of τ.

    The triple (X,τ,E) is called a soft topological space. A member in τ is called soft open and its relative complement is called soft closed.

    Proposition 2.12. [32] In (X,τ,E), a family τe={G(e):GEτ} is a classical topology on X for each eE.

    τe is called a parametric topology and (X,τe) is called a parametric topological space.

    Definition 2.13. [32] Let (X,τ,E) be a soft topological space and YX. A family τY={˜Y˜GE:GEτ} is called a soft relative topology on Y and the triple (Y,τY,E) is called a soft subspace of (X,τ,E).

    Definition 2.14. [3] A subset GE of (X,τ,E) is called soft α-open if GE˜int(cl(int(GE))).

    The following result will help us to establish some properties of soft α-separation axioms and soft α-compact spaces, see, for example, Theorem (3.16) and Proposition (3.24). It implies that the family of soft α-open subsets of (X,τ,E) forms a new soft topology τα over X that is finer than τ. In fact, this characteristic of soft α-open sets that does not exist for the families of soft semi-open, soft pre-open, soft b-open and soft β-open sets.

    Theorem 2.15. [3,8]

    (ⅰ) Every soft open set is soft α-open.

    (ⅱ) The arbitrary union (finite intersection) of soft α-open sets is soft α-open.

    Definition 2.16. [3] Let GE be a subset of (X,τ,E). Then ¯GEα is the intersection of all soft α-closed sets containing GE.

    It is clear that: x¯GEα if and only if GE˜UE˜Φ for each soft α-open set UE totally containing x; and Pxe¯GEα if and only if GE˜UE˜Φ for each soft α-open set UE totally containing Pxe.

    Proposition 2.17. [8] Let ˜Y be soft open subset of (X,τ,E). Then:

    1. If (H,E) is soft α-open and ˜Y is soft open in (X,τ,E), then (H,E)˜(Y,E) is a soft α-open subset of (Y,τY,E).

    2. If ˜Y is soft open in (X,τ,E) and (H,E) is a soft α-open in (Y,τY,E), then (H,E) is a soft α-open subset of (X,τ,E).

    Definition 2.18. [4] (X,τ,E) is said to be:

    (ⅰ) soft αT0 if for every xyX, there is a soft α-open set UE such that xUE and yUE; or yUE and xUE.

    (ⅱ) soft αT1 if for every xyX, there are two soft α-open sets UE and VE such that xUE and yUE; and yVE and xVE.

    (ⅲ) soft αT2 if for every xyX, there are two disjoint soft α-open sets UE and VE such that xGE and yFE.

    (ⅳ) soft α-regular if for every soft α-closed set HE and xX such that xHE, there are two disjoint soft α-open sets UE and VE such that HE˜UE and xVE.

    (ⅴ) soft α-normal if for every two disjoint soft α-closed sets HE and FE, there are two disjoint soft α-open sets UE and VE such that HE˜UE and FE˜VE.

    (ⅵ) soft αT3 (resp. soft αT4) if it is both soft α-regular (resp. soft α-normal) and soft αT1-space.

    Definition 2.19. [8] A family {GiE:iI} of soft α-open subsets of (X,τ,E) is said to be a soft α-open cover of ˜X if ˜X=˜iIGiE.

    Definition 2.20. [8] (X,τ,E) is said to be:

    (ⅰ) soft αT2 if for every PxePye˜X, there are two disjoint soft α-open sets UE and VE containing Pxe and Pye, respectively.

    (ⅱ) soft α-compact if every soft α-open cover of ˜X has a finite subcover.

    Proposition 2.21. [8]

    (ⅰ) A soft α-compact subset of a soft αT2-space is soft α-closed.

    (ⅱ) A stable soft α-compact subset of a soft αT2-space is soft α-closed.

    To study the properties that preserved under soft α-homeomorphism maps, the concept of a soft α-irresolute map will be presented in this work under the name of a soft α-continuous map.

    Definition 2.22. [8] gφ:(X,τ,E)(Y,θ,E) is called soft α-continuous if the inverse image of each soft α-open set is soft α-open.

    Proposition 2.23. [8] The soft α-continuous image of a soft α-compact set is soft α-compact.

    Definition 2.24. [3] A soft map fφ:(X,τ,A)(Y,θ,B) is said to be:

    (ⅰ) soft α-continuous if the inverse image of each soft open set is soft α-open.

    (ⅱ) soft α-open (resp. soft α-closed) if the image of each soft open (resp. soft closed) set is soft α-open (resp. soft α-closed).

    (ⅲ) a soft α-homeomorphism if it is bijective, soft α-continuous and soft α-open.

    Definition 2.25. A soft topology τ on X is said to be:

    (ⅰ) an enriched soft topology [14] if all soft sets GE such that G(e)= or X are members of τ.

    (ⅱ) an extended soft topology [31] if τ={GE:G(e)τe for each eE}, where τe is a parametric topology on X.

    Al-shami and Kočinac [12] proved the equivalence of enriched and extended soft topologies and obtained many useful results that help to study the relationships between soft topological spaces and their parametric topological spaces.

    Theorem 2.26. [12] A subset (F,E) of an extended soft topological space (X,τ,E) is soft α-open if and only if each e-approximate element of (F,E) is α-open.

    Proposition 2.27. [13] Let {(Xi,τi,E):iI} be a family of pairwise disjoint soft topological spaces and X=iIXi. Then the collection

    τ={(G,E)˜˜X:(G,E)˜~Xiisasoftopensetin(Xi,τi,E)foreveryiI}

    defines a soft topology on X with a fixed set of parameters E.

    Definition 2.28. [13] The soft topological space (X,τ,E) given in the above proposition is said to be the sum of soft topological spaces and is denoted by (iIXi,τ,E).

    Theorem 2.29. [13] A soft set (G,E)˜~iIXi is soft α-open (resp. soft α-closed) in (iIXi,τ,E) if and only if all (G,E)˜~Xi are soft α-open (resp. soft α-closed) in (Xi,τi,E).

    Proposition 2.30. [36] Let gφ:(X,τ,E)(X,τ,E) be a soft map such that ˜nNgnφ(˜X) is a soft point Pxe. Then Pxe is a unique fixed point of gφ.

    Theorem 2.31. [38] Let (X,τ,A) and (Y,θ,B) be two soft topological spaces and Ω={GA×FB:GAτ and FBθ}. Then the family of all arbitrary union of elements of Ω is a soft topology over X×Y under a fixed set of parameters A×B.

    Lemma 2.32. [7] Let (G,A) and (H,B) be two subsets of (X1,τ1,A) and (X2,τ2,B), respectively. Then:

    (ⅰ) cl(G,A)×cl(H,B)=cl((G,A)×(H,B)).

    (ⅱ) int(G,A)×int(H,B)=int((G,A)×(H,B)).

    This section introduces the concepts of tt-soft αTi(i=0,1,2,3,4) and tt-soft α-regular spaces, where tt denote the total belong and total non-belong relations that are utilized in the definitions of these concepts. The relationships between them are showed and their main features are studied. In addition, their behaviours with the concepts of hereditary, topological and additive properties are investigated. Some examples are provided to elucidate the obtained results.

    Definition 3.1. (X,τ,E) is said to be:

    (ⅰ) tt-soft αT0 if for every xyX, there exists a soft α-open set UE such that xUE and y⋐̸UE or yUE and x⋐̸UE.

    (ⅱ) tt-soft αT1 if for every xyX, there exist soft α-open sets UE and VE such that xUE and y⋐̸UE; and yVE and x⋐̸VE.

    (ⅲ) tt-soft αT2 if for every xyX, there exist two disjoint soft α-open sets UE and VE such that xUE and y⋐̸UE; and yVE and x⋐̸VE.

    (ⅳ) tt-soft α-regular if for every soft α-closed set HE and xX such that x⋐̸HE, there exist disjoint soft α-open sets UE and VE such that HE˜UE and xVE.

    (ⅴ) tt-soft αT3 (resp. tt-soft αT4) if it is both tt-soft α-regular (resp. soft α-normal) and tt-soft αT1.

    Remark 3.2. It can be noted that: If FE and GE are disjoint soft set, then xFE if and only if x⋐̸GE. This implies that (X,τ,E) is a tt-soft αT2-space if and only if is a soft αT2-space. That is, the concepts of a tt-soft αT2-space and a soft αT2-space are equivalent.

    We can say that: (X,τ,E) is tt-soft αT2 if for every xyX, there exist two disjoint soft α-open sets UE and VE totally contain x and y, respectively.

    Remark 3.3. The soft α-regular spaces imply a strict condition on the shape of soft α-open and soft α-closed subsets. To explain this matter, let FE be a soft α-closed set such that xHE. Then we have two cases:

    (ⅰ) There are e,eE such that xH(e) and xH(e). This case is impossible because there do not exist two disjoint soft sets UE and VE containing x and HE, respectively.

    (ⅱ) For each eE, xH(e). This implies that HE must be stable.

    As a direct consequence, we infer that every soft α-closed and soft α-open subsets of a soft α-regular space must be stable. However, this matter does not hold on the tt-soft α-regular spaces because we replace a partial non-belong relation by a total non-belong relation. Therefore a tt-soft α-regular space need not be stable.

    Proposition 3.4. (ⅰ) Every tt-soft αTi-space is soft αTi for i=0,1,4.

    (ⅱ) Every soft α-regular space is tt-soft α-regular.

    (ⅲ) Every soft αT3-space is tt-soft αT3.

    Proof. The proofs of (ⅰ) and (ⅱ) follow from the fact that a total non-belong relation ⋐̸ implies a partial non-belong relation .

    To prove (ⅲ), it suffices to prove that a soft αTi-space is tt-soft αTi when (X,τ,E) is soft α-regular. Suppose xyX. Then there exist two soft α-open sets UE and VE such that xUE and yUE; and yVE and xVE. Since UE and VE are soft α-open subsets of a soft α-regular space, then they are stable. So y⋐̸UE and x⋐̸VE. Thus (X,τ,E) is tt-soft αT1. Hence, we obtain the desired result.

    To clarify that the converse of the above proposition does not hold in general, we give the following examples.

    Example 3.5. Let E={e1,e2} and τ={˜Φ,˜X,GiE:i=1,2,3} be a soft topology on X={x,y}, where

    G1E={(e1,{x}),(e2,X)};G2E={(e1,X),(e2,{y})}andG3E={(e1,{x}),(e2,{y})}.

    One can examine that τ=τα. Then (X,τ,E) is a soft αT1-space. On the other hand, it is not tt-soft αT0 because there does not exist a soft α-open set containing one of the points x or y such that the other point does not totally belong to it.

    Example 3.6. Let E={e1,e2} and τ={˜Φ,˜X,GiE:i=1,2,...,8} be a soft topology on X={x,y}, where

    G1E={(e1,X),(e2,{x})};G2E={(e1,),(e2,{y})};G3E={(e1,{y}),(e2,)};G4E={(e1,{y}),(e2,{y})};G5E={(e1,{x}),(e2,{y})};G6E={(e1,X),(e2,{y})};G7E={(e1,{x}),(e2,)}andG8E={(e1,X),(e2,)}.

    By calculating, we find that τα=τ.

    Then (X,τ,E) is a soft αT4-space. On the other hand, there does not exist a soft α-open set totally containing x such that y does not totally belong to it. So (X,τ,E) is not a tt-soft αT1-space, hence it is not tt-soft αT4.

    Example 3.7. Let X be any universal set X and E be any set of parameters such that |X|2 and |E|2. The discrete soft topology (X,τ,E) is a tt-soft α-regular space, but it is not soft α-regular. Hence, it is a tt-soft αT3-space, but it is not soft αT3.

    Before we show the relationship between tt-soft αTi-spaces, we need to prove the following useful lemma.

    Lemma 3.8. (X,τ,E) is a tt-soft αT1-space if and only if xE is soft α-closed for every xX.

    Proof. Necessity: For each yiX{x}, there is a soft α-open set GiE such that yiGiE and x⋐̸GiE. Therefore X{x}=iIGi(e) and x⋐̸iIGi(e) for each eE. Thus ˜iIGiE=~X{x} is soft α-open. Hence, xE is soft α-closed.

    Sufficiency: Let xy. By hypothesis, xE and yE are soft α-closed sets. Then xcE and ycE are soft α-open sets such that x(yE)c and y(xE)c. Obviously, y⋐̸(yE)c and x⋐̸(xE)c. Hence, (X,τ,E) is tt-soft αT1.

    Proposition 3.9. Every tt-soft αTi-space is tt-soft αTi1 for i=1,2,3,4.

    Proof. We prove the proposition in the cases of i=3,4. The other cases follow similar lines.

    For i=3, let xy in a tt-soft αT3-space (X,τ,E). Then xE is soft α-closed. Since y⋐̸xE and (X,τ,E) is tt-soft α-regular, then there are disjoint soft α-open sets GE and FE such that xE˜GE and yFE. Therefore (X,τ,E) is tt-soft αT2.

    For i=4, let xX and HE be a soft α-closed set such that x⋐̸HE. Since (X,τ,E) is tt-soft αT1, then xE is soft α-closed. Since xE˜HE=˜Φ and (X,τ,E) is soft α-normal, then there are disjoint soft α-open sets GE and FE such that HE˜GE and xE˜FE. Hence, (X,τ,E) is tt-soft αT3.

    The following examples show that the converse of the above proposition is not always true.

    Example 3.10. Let (X,τ,E) be a soft topological space given in Example (3.6). For xy, we have G4E is a soft α-open set such that yG4E and x⋐̸G4E. Then (X,τ,E) is tt-soft αT0. However, it is not tt-soft αT1 because there does not exist a soft α-open set totally containing x and does not totally contain y.

    Example 3.11. Let E be any set of parameters and τ={˜Φ,GE˜N:GcE is finite} be a soft topology on the set of natural numbers N. It is clear that a soft subset of (N,τ,E) is soft α-open if and only if it is soft open. For each xyN, we have ~N{y} and ~N{x} are soft α-open sets such that x~N{y} and y⋐̸~N{y}; and y~N{x} and x⋐̸~N{x}. Therefore (N,τ,E) is tt-soft αT1. On the other hand, there do not exist two disjoint soft α-open sets except for the null and absolute soft sets. Hence, (N,τ,E) is not tt-soft αT2.

    Example 3.12. It is well known that a soft topological space is a classical topological space if E is a singleton. Then it suffices to consider examples that satisfy an αT2-space but not αT3; satisfy an αT3-space but not αT4.

    In what follows, we establish some properties of tt-soft αTi and tt-soft α-regular.

    Lemma 3.13. Let UE be a subset of (X,τ,E) and xX. Then x⋐̸¯UEα iff there exists a soft α-open set VE totally containing x such that UE˜VE=˜Φ.

    Proof. Let x⋐̸¯UEα. Then x(¯UEα)c=VE. So UE˜VE=˜Φ. Conversely, if there exists a soft α-open set VE totally containing x such that UE˜VE=˜Φ, then UEVcE. Therefore ¯UEαVcE. Since x⋐̸VcE, then x⋐̸¯UEα.

    Proposition 3.14. If (X,τ,E) is a tt-soft αT0-space, then ¯xEα¯yEα for every xyX.

    Proof. Let xy in a tt-soft αT0-space. Then there is a soft α-open set UE such that xUE and y⋐̸UE or yUE and x⋐̸UE. Say, xUE and y⋐̸UE. Now, yE˜UE=˜Φ. So, by the above lemma, x⋐̸¯yEα. But x¯xEα. Hence, we obtain the desired result.

    Corollary 3.15. If (X,τ,E) is a tt-soft αT0-space, then ¯Pxeα¯Pyeα for all xy and e,eE.

    Theorem 3.16. Let E be a finite set. Then (X,τ,E) is a tt-soft αT1-space if and only if xE=˜{UE:xUEτα} for each xX.

    Proof. To prove the "if" part, let yX. Then for each xX{y}, we have a soft α-open set UE such that xUE and y⋐̸UE. Therefore y⋐̸˜{UE:xE˜UEτα}. Since y is chosen arbitrary, then the desired result is proved.

    To prove the "only if" part, let the given conditions be satisfied and let xy. Let E∣=m. Since y⋐̸xE, then for each j=1,2,...,m there is a soft α-open set UiE such that y\not\in U_{i}(e_j) and x\in U_{{i}_E} . Therefore \widetilde{\bigcap}_{i = 1}^{m} U_{{i}_E} is a soft \alpha -open set such that y\not\Subset\widetilde{\bigcap}_{i = 1}^{m} U_{{i}_E} and x\in\widetilde{\bigcap}_{i = 1}^{m} U_{{i}_E} . Similarly, we can get a soft \alpha -open set V_E such that y\in V_E and x\not\Subset V_E . Thus (X, \tau, E) is a tt -soft \alpha T_1 -space.

    Theorem 3.17. If (X, \tau, E) is an extended tt -soft \alpha T_1 -space, then P^x_e is soft \alpha -closed for all P^x_e\in \widetilde{X} .

    Proof. It follows from Lemma (3.8) that \widetilde{X\backslash \{x\}} is a soft \alpha -open set. Since (X, \tau, E) is extended, then a soft set H_E , where H(e) = \emptyset and H(e') = X for each e'\neq e , is a soft \alpha -open set. Therefore \widetilde{X\backslash \{x\}}\widetilde{\bigcup} H_E is soft \alpha -open. Thus (\widetilde{X\backslash \{x\}}\widetilde{\bigcup} H_E)^c = P^x_{e} is soft \alpha -closed.

    Corollary 3.18. If (X, \tau, E) is an extended tt -soft \alpha T_1 -space, then the intersection of all soft \alpha -open sets containing U_E is exactly U_E for each U_E \widetilde{\subseteq}\widetilde{X} .

    Proof. Let U_E be a soft subset of \widetilde{X} . Since P^x_e is a soft \alpha -closed set for every P^x_e\in U^c_E , then \widetilde{X}\setminus P^x_e is a soft \alpha -open set containing U_E . Therefore U_E = \widetilde{\bigcap}\{\widetilde{X}\setminus P^x_e: P^x_e\in U^c_E\} , as required.

    Theorem 3.19. A finite (X, \tau, E) is tt -soft \alpha T_2 if and only if it is tt -soft \alpha T_1 .

    Proof. Necessity: It is obtained from Proposition (3.9).

    Sufficiency: For each x\neq y , we have x_E and y_E are soft \alpha -closed sets. Since X is finite, then \widetilde{\bigcup}_{y\in X\backslash \{x\}} y_E and \widetilde{\bigcup}_{x\in X\backslash \{y\}} x_E are soft \alpha -closed sets. Therefore (\widetilde{\bigcup}_{y\in X\backslash\{x\}}y_E)^c = x_E and (\widetilde{\bigcup}_{x\in X\backslash\{y\}} x_E)^c = y_E are disjoint soft \alpha -open sets. Thus (X, \tau, E) is a tt -soft \alpha T_2 -space.

    Corollary 3.20. A finite tt -soft \alpha T_1 -space is soft \alpha -disconnected.

    Remark 3.21. In Example (3.11), note that x_E is not a soft \alpha -open set for each x\in \mathbb{N} . This clarifies that a soft set x_E in a tt -soft \alpha T_1 -space need not be soft \alpha -open if the universal set is infinite.

    Theorem 3.22. (X, \tau, E) is tt -soft \alpha -regular iff for every soft \alpha -open subset F_E of (X, \tau, E) totally containing x , there is a soft \alpha -open set V_E such that x\in V_E \widetilde{\subseteq}\overline{V_E}^{\alpha} \widetilde{\subseteq} F_E .

    Proof. Let x\in X and F_E be a soft \alpha -open set totally containing x . Then F^c_E is \alpha -soft closed and x_E\widetilde{\bigcap}F^c_E = \widetilde{\Phi} . Therefore there are disjoint soft \alpha -open sets U_E and V_E such that F^c_E\widetilde{\subseteq}U_ E and x\in V_E . Thus V_E\widetilde{\subseteq} U^c_E\widetilde{\subseteq} F_E . Hence, \overline{V_E}^{\alpha}\widetilde{\subseteq} U^c_E\widetilde{\subseteq} F_E . Conversely, let F^c_E be a soft \alpha -closed set. Then for each x\not\Subset F^c_E , we have x\in F_E . By hypothesis, there is a soft \alpha -open set V_E totally containing x such that \overline{V_E}^{\alpha}\widetilde{\subseteq} F_E . Therefore F^c_E\widetilde{\subseteq} (\overline{V_E}^{\alpha})^c and V_E\widetilde{\bigcap}(\overline{V_E}^{\alpha})^c = \widetilde{\Phi} . Thus (X, \tau, E) is tt -soft \alpha -regular, as required.

    Theorem 3.23. The following properties are equivalent if (X, \tau, E) is a tt -soft \alpha -regular space.

    (ⅰ) a tt -soft \alpha T_2 -space.

    (ⅱ) a tt -soft \alpha T_1 -space.

    (ⅲ) a tt -soft \alpha T_0 -space.

    Proof. The directions {\bf{(i)}}\rightarrow {\bf{(ii)}} and {\bf{(ii)}}\rightarrow{\bf{(iii)}} are obvious.

    To prove {\bf{(iii)}}\rightarrow {\bf{(i)}} , let x\neq y in a tt -soft \alpha T_0 -space (X, \tau, E) . Then there exists a soft \alpha -open set G_E such that x\in G_E and y\not\Subset G_E , or y\in G_E and x\not\Subset G_E . Say, x\in G_E and y\not\Subset G_E . Obviously, x\not\Subset G^c_E and y\in G^c_E . Since (X, \tau, E) is tt -soft \alpha -regular, then there exist two disjoint soft \alpha -open sets U_E and V_E such that x\in U_E and y\in G^c_E\widetilde{\subseteq} V_E . Hence, (X, \tau, E) is tt -soft \alpha T_2 .

    Proposition 3.24. A finite tt -soft \alpha T_{2} -space (X, \tau, E) is tt -soft \alpha -regular.

    Proof. Let H_E be a soft \alpha -closed set and x\in X such that x\not\Subset H_E . Then x\neq y for each y\Subset H_E . By hypothesis, there are two disjoint soft \alpha -open sets U_{i_E} and V_{i_E} such that x\in U_{i_E} and y\in V_{i_E} . Since \{y:y\in X\} is a finite set, then there is a finite number of soft \alpha -open sets V_{i_E} such that H_E\widetilde{\subseteq}\widetilde{\bigcup}_{i = 1}^{m}V_{i_E} . Now, \widetilde{\bigcap}_{i = 1}^{m} U_{i_E} is a soft \alpha -open set containing x and [\widetilde{\bigcup}_{i = 1}^{m}V_{i_E} ]\widetilde{\bigcap}[\widetilde{\bigcap}_{i = 1}^{m}U_{i_E}] = \widetilde{\Phi} . Hence, (X, \tau, E) is tt -soft \alpha -regular.

    Corollary 3.25. The following properties are equivalent if (X, \tau, E) is finite.

    (ⅰ) a tt -soft \alpha T_{3} -space.

    (ⅱ) a tt -soft \alpha T_{2} -space.

    (ⅲ) a tt -soft \alpha T_{1} -space.

    Proof. The directions {\bf{(i)}}\rightarrow {\bf{(ii)}} and {\bf{(ii)}}\rightarrow {\bf{(iii)}} follow from Proposition (3.9).

    The direction {\bf{(iii)}}\rightarrow {\bf{(ii)}} follows from Theorem (3.19).

    The direction {\bf{(ii)}}\rightarrow {\bf{(i)}} follows from Proposition (3.24).

    Theorem 3.26. The property of being a tt -soft \alpha T_i -space (i = 0, 1, 2, 3) is a soft open hereditary.

    Proof. We prove the theorem in the case of i = 3 and the other cases follow similar lines.

    Let (Y, \tau_Y, E) be a soft open subspace of a tt -soft \alpha T_3 -space (X, \tau, E) . To prove that (Y, \tau_Y, E) is tt -soft \alpha T_{1} , let x\neq y \in Y . Since (X, \tau, E) is a tt -soft \alpha T_{1} -space, then there exist two soft \alpha -open sets G_E and F_E such that x\in G_E and y\not\Subset G_E ; and y\in F_E and x\not\Subset F_E . Therefore x\in U_E = \widetilde{Y}\widetilde{\bigcap} G_E and y\in V_E = \widetilde{Y}\widetilde{\bigcap} F_E such that y\not\Subset U_E and x\not\Subset V_E . It follows from Proposition (2.17), that U_E and V_E are soft \alpha -open subsets of (Y, \tau_{Y}, E) , so that (Y, \tau_Y, E) is tt -soft \alpha T_{1} .

    To prove that (Y, \tau_Y, E) is tt -soft \alpha -regular, let y\in Y and F_E be a soft \alpha -closed subset of (Y, \tau_Y, E) such that y\not\Subset F_E . Then F_E\widetilde{\bigcup}\widetilde{Y^c} is a soft \alpha -closed subset of (X, \tau, E) such that y\not\Subset F_E\widetilde{\bigcup}\widetilde{Y^c} . Therefore there exist disjoint soft \alpha -open subsets U_E and V_E of (X, \tau, E) such that F_E\widetilde{\bigcup}\widetilde{Y^c}\widetilde{\subseteq} U_E and y\in V_E . Now, U_E\widetilde{\bigcap}\widetilde{Y} and V_E\widetilde{\bigcap}\widetilde{Y} are disjoint soft \alpha -open subsets of (Y, \tau_{Y}, E) such that F_E\widetilde{\subseteq} U_E\widetilde{\bigcap}\widetilde{Y} and y\in V_E\widetilde{\bigcap}\widetilde{Y} . Thus (Y, \tau_Y, E) is tt -soft \alpha -regular.

    Hence, (Y, \tau_Y, E) is tt -soft \alpha T_{3} , as required.

    Theorem 3.27. Let (X, \tau, E) be extended and i = 0, 1, 2, 3, 4 . Then (X, \tau, E) is tt -soft \alpha T_i iff (X, \tau_{e}) is \alpha T_i for each e\in E .

    Proof. We prove the theorem in the case of i = 4 and one can similarly prove the other cases.

    Necessity: Let x\neq y in X . Then there exist two soft \alpha -open sets U_E and V_E such that x\in U_E and y\not\Subset U_E ; and y\in V_E and x\not\Subset V_E . Obviously, x\in U(e) and y\not\in U(e) ; and y\in V(e) and x\not\in V(e) . Since (X, \tau, E) is extended, then it follows from Theorem (2.26) that U(e) and V(e) are \alpha -open subsets of (X, \tau_e) for each e\in E . Thus, (X, \tau_e) is an \alpha T_1 -space. To prove that (X, \tau_{e}) is \alpha -normal, let F_e and H_e be two disjoint \alpha -closed subsets of (X, \tau_{e}) . Let F_E and H_E be two soft sets given by F(e) = F_e , H(e) = H_e and F(e') = H(e') = \emptyset for each e'\neq e . It follows, from Theorem (2.26) that F_E and H_E are two disjoint soft \alpha -closed subsets of (X, \tau, E) . By hypothesis, there exist two disjoint soft \alpha -open sets G_E and W_E such that F_E\widetilde{\subseteq}G_E and H_E\widetilde{\subseteq}W_E . This implies that F(e) = F_e\subseteq G(e) and H(e) = H_e\subseteq W(e) . Since (X, \tau, E) is extended, then it follows from Theorem (2.26) that G(e) and W(e) are \alpha -open subsets of (X, \tau_e) . Thus, (X, \tau_e) is an \alpha -normal space. Hence, it is an \alpha T_4 -space.

    Sufficiency: Let x\neq y in X . Then there exists two \alpha -open subsets U_e and V_e of (X, \tau_e) such that x\in U_e and y\not\in U_e ; and y\in V_e and x\not\in V_e . Let U_E and V_E be two soft sets given by U(e) = U_e , V(e) = V_e for each e\in E . Since (X, \tau, E) is extended, then it follows from Theorem (2.26) that U_E and V_E are soft \alpha -open subsets of (X, \tau, E) such that x\in U_E and y\not\Subset U_E ; and y\in V_E and x\not\Subset V_E . Thus, (X, \tau, E) is a tt -soft \alpha T_1 -space. To prove that (X, \tau, E) is soft \alpha -normal, let F_E and H_E be two disjoint soft \alpha -closed subsets of (X, \tau, E) . Since (X, \tau, E) is extended, then it follows from Theorem (2.26) that F(e) and H(e) are two disjoint \alpha -closed subsets of (X, \tau_e) . By hypothesis, there exist two disjoint \alpha -open subsets G_e and W_e of (X, \tau_e) such that F(e)\subseteq G_e and H(e)\subseteq W_e . Let G_E and W_E be two soft sets given by G(e) = G_e and W(e) = W_e for each e\in E . Since (X, \tau, E) is extended, then it follows from Theorem (2.26) that G_E and W_E are two disjoint soft \alpha -open subsets of (X, \tau, E) such that F_E\widetilde{\subseteq} G_E and H_E\widetilde{\subseteq} W_E . Thus (X, \tau, E) is soft \alpha -normal. Hence, it is a tt -soft \alpha T_4 -space.

    In the following examples, we show that a condition of an extended soft topology given in the above theorem is not superfluous.

    Example 3.28. Let E = \{e_1, e_2\} and \tau = \{\widetilde{\Phi}, \widetilde{X}, G_{1_E}, G_{2_E}\} be a soft topology on X = \{x, y\} , where

    G_{1_E} = \{(e_1, \{x\}), (e_2, \{y\})\} \;and \\ G_{2_E} = \{(e_1, \{y\}), (e_2, \{x\})\} .

    One can examine that \tau = \tau^{\alpha} . It is clear that (X, \tau, E) is not a tt -soft \alpha T_0 -space. On the other hand, \tau_{e_1} and \tau_{e_2} are the discrete topology on X . Hence, the two parametric topological spaces (X, \tau_{e_1}) and (X, \tau_{e_2}) are \alpha T_4 .

    Theorem 3.29. The property of being a tt -soft \alpha T_i -space (i = 0, 1, 2) is preserved under a finite product soft spaces.

    Proof. We prove the theorem in case of i = 2 . The other cases follow similar lines.

    Let (X_1, \tau_1, E_1) and (X_2, \tau_2, E_2) be two tt -soft \alpha T_2 -spaces and let (x_1, y_1)\neq(x_2, y_2) in X_1\times X_2 . Then x_1\neq x_2 or y_1\neq y_2 . Without loss of generality, let x_1\neq x_2 . Then there exist two disjoint soft \alpha -open subsets G_{E_1} and H_{E_1} of (X_1, \tau_1, E_1) such that x_1\in G_{E_1} and x_2\not\Subset G_{E_1} ; and x_2\in H_{E_1} and x_1\not\Subset H_{E_1} . Obviously, G_{E_1}\times\widetilde{X_2} and H_{E_1}\times\widetilde{X_2} are two disjoint soft \alpha -open subsets X_1\times X_2 such that (x_1, y_1)\in G_{E_1}\times\widetilde{X_2} and (x_2, y_2)\not\Subset G_{E_1}\times\widetilde{X_2} ; and (x_2, y_2)\in H_{E_1}\times\widetilde{X_2} and (x_1, y_1)\not\Subset H_{E_1}\times\widetilde{X_2} . Hence, X_1\times X_2 is a tt -soft \alpha T_2 -space.

    Theorem 3.30. The property of being a tt -soft \alpha T_i -space is an additive property for i = 0, 1, 2, 3, 4 .

    Proof. To prove the theorem in the cases of i = 2 . Let x\neq y\in \oplus_{i\in I}X_i . Then we have the following two cases:

    1. There exists i_0\in I such that x, y\in X_{i_0} . Since (X_{i_0}, \tau_{i_0}, E) is tt -soft \alpha T_2 , then there exist two disjoint soft \alpha -open subsets G_E and H_E of (X_{i_0}, \tau_{i_0}, E) such that x\in G_E and y\in H_E . It follows from Theorem (2.29), that G_E and H_E are disjoint soft \alpha -open subsets of (\oplus_{i\in I}X_i, \tau, E) .

    2. There exist i_0\neq j_0\in I such that x\in X_{i_0} and y\in X_{j_0} . Now, \widetilde{X_{i_0}} and \widetilde{X_{j_0}} are soft \alpha -open subsets of (X_{i_0}, \tau_{i_0}, E) and (X_{j_0}, \tau_{j_0}, E) , respectively. It follows from Theorem (2.29), that \widetilde{X_{i_0}} and \widetilde{X_{j_0}} are disjoint soft \alpha -open subsets of (\oplus_{i\in I} X_i, \tau, E) .

    It follows from the two cases above that (\oplus_{i\in I}X_i, \tau, E) is a tt -soft \alpha T_2 -space.

    The theorem can be proved similarly in the cases of i = 0, 1 .

    To prove the theorem in the cases of i = 3 and i = 4 , it suffices to prove the tt -soft \alpha -regularity and soft \alpha -normality, respectively.

    First, we prove the tt -soft \alpha -regularity property. Let F_E be a soft \alpha -closed subset of (\oplus_{i\in I}X_i, \tau, E) such that x\not\Subset F_E . It follows from Theorem (2.29) that F_E\widetilde{\bigcap}\widetilde{X_i} is soft \alpha -closed in (X_i, \tau_i, E) for each i\in I . Since x\in \oplus_{i\in I} X_i , there is only i_0\in I such that x\in X_{i_0} . This implies that there are disjoint soft \alpha -open subsets G_E and H_E of (X_{i_0}, \tau_{i_0}, E) such that F_E\widetilde{\bigcap}\widetilde{X_{i_0}}\widetilde{\subseteq} G_E and y\in H_E . Now, G_E\widetilde{\bigcup\limits_{i\neq i_0}}\widetilde{X_i} is a soft \alpha -open subset of (\oplus_{i\in I}X_i, \tau, E) containing F_E . The disjointness of G_E\bigcup_{i\neq i_0}X_i and H_E ends the proof that (\oplus_{i\in I}X_i, \tau, E) is a tt -soft \alpha -regular space.

    Second, we prove the soft \alpha -normality property. Let F_E and H_E be two disjoint soft \alpha -closed subsets of (\oplus_{i\in I}X_i, \tau, E) . It follows from Theorem (2.29) that F_E\widetilde{\bigcap}\widetilde{X_i} and H_E\widetilde{\bigcap}\widetilde{X_i} are soft \alpha -closed in (X_i, \tau_i, E) for each i\in I . Since (X_i, \tau_i, E) is soft \alpha -normal for each i\in I , then there there exist two disjoint soft \alpha -open subsets U_{i_E} and V_{i_E} of (X_i, \tau_i, E) such that F_E\widetilde{\bigcap}\widetilde{X_i}\widetilde{\subseteq} U_{i_E} and H_E\widetilde{\bigcap}\widetilde{X_i}\widetilde{\subseteq} V_{i_E} . This implies that F_E\widetilde{\subseteq}\widetilde{\bigcup\limits_{i\in I}}U_{i_E} , H_E\widetilde{\subseteq}\widetilde{\bigcup\limits_{i\in I}} V_{i_E} and [\widetilde{\bigcup\limits_{i\in I}}U_{i_E}]\widetilde{\bigcap}[\widetilde{\bigcup\limits_{i\in I}} V_{i_E}] = \widetilde{\Phi} . Hence, (\oplus_{i\in I}X_i, \tau, E) is a soft \alpha -normal space.

    In the following we probe the behaviours of tt -soft \alpha T_i -spaces under some soft maps.

    Definition 3.31. A map f_{\varphi}:(X, \tau, A)\rightarrow (Y, \theta, B) is said to be:

    1. soft \alpha^{\star} -continuous if the inverse image of soft \alpha -open set is soft \alpha -open.

    2. soft \alpha^{\star} -open (resp. soft \alpha^{\star} -closed) if the image of soft \alpha -open (resp. soft \alpha -closed) set is soft \alpha -open (resp. soft \alpha -closed).

    3. soft \alpha^{\star} -homeomorphism if it is bijective, soft \alpha^{\star} -continuous and soft \alpha^{\star} -open.

    Proposition 3.32. Let f_{\varphi}:(X, \tau, A)\rightarrow (Y, \theta, B) be a soft \alpha -continuous map such that f is injective. Then if (Y, \theta, B) is a p -soft T_i -space, then (X, \tau, A) is a tt -soft \alpha T_i -space for i = 0, 1, 2 .

    Proof. We only prove the proposition for i = 2 .

    Let f_{\varphi}:(X, \tau, A)\rightarrow (Y, \theta, B) be a soft \alpha -continuous map and a\neq b\in X . Since f is injective, then there are two distinct points x and y in Y such that f(a) = x and f(b) = y . Since (Y, \theta, B) is a p -soft T_2 -space, then there are two disjoint soft open sets G_B and F_B such that x\in G_B and y\in F_B . Now, f_{\varphi}^{-1}(G_B) and f_{\varphi}^{-1}(F_B) are two disjoint soft \alpha -open subsets of (X, \tau, A) such that a\in f_{\varphi}^{-1}(G_B) and b\in f_{\varphi}^{-1}(F_B) . Thus (X, \tau, A) is a tt -soft \alpha T_2 -space.

    In a similar way, one can prove the following result.

    Proposition 3.33. Let f_{\varphi}:(X, \tau, A)\rightarrow (Y, \theta, B) be a soft \alpha^{\star} -continuous map such that f is injective. Then if (Y, \theta, B) is a tt -soft \alpha T_i -space, then (X, \tau, A) is a tt -soft \alpha T_i -space for i = 0, 1, 2 .

    Proposition 3.34. Let f_{\varphi}:(X, \tau, A)\rightarrow (Y, \theta, B) be a bijective soft \alpha -open map. Then if (X, \tau, A) is a p -soft T_i -space, then (Y, \theta, B) is a tt -soft \alpha T_i -space for i = 0, 1, 2 .

    Proof. We only prove the proposition for i = 2 .

    Let f_{\varphi}:(X, \tau, A)\rightarrow (Y, \theta, B) be a soft \alpha -open map and x\neq y\in Y . Since f is bijective, then there are two distinct points a and b in X such that a = f^{-1}(x) and b = f^{-1}(y) . Since (X, \tau, A) is a p -soft T_2 -space, then there are two disjoint soft open sets U_A and V_A such that x\in U_A and y\in V_A . Now, f_{\varphi}(U_A) and f_{\varphi}(V_A) are two disjoint soft \alpha -open subsets of (Y, \theta, B) such that x\in f_{\varphi}(U_A) and y\in f_{\varphi}(V_A) . Thus (Y, \theta, B) is a tt -soft \alpha T_2 -space.

    In a similar way, one can prove the following result.

    Proposition 3.35. Let f_{\varphi}:(X, \tau, A)\rightarrow (Y, \theta, B) be a bijective soft \alpha^{\star} -open map. Then if (X, \tau, A) is a tt -soft \alpha T_i -space, then (Y, \theta, B) is a tt -soft \alpha T_i -space for i = 0, 1, 2 .

    Proposition 3.36. The property of being tt -soft \alpha T_i \; (i = 0, 1, 2, 3, 4) is preserved under a soft \alpha^{\star} -homeomorphism map.

    We complete this section by discussing some interrelations between tt -soft \alpha T_i -spaces (i = 2, 3, 4) and soft \alpha -compact spaces.

    Proposition 3.37. A stable soft \alpha -compact subset of a tt -soft \alpha T_2 -space is soft \alpha -closed.

    Proof. It follows from Proposition (2.21) and Remark (3.2).

    Theorem 3.38. Let H_E be a soft \alpha -compact subset of a tt -soft \alpha T_2 -space. If x\not\Subset H_E , then there are disjoint soft \alpha -open sets U_E and V_E such that x\in U_E and H_E\subseteq V_E .

    Proof. Let x\not\Subset H_E . Then x\neq y for each y\Subset H_E . Since (X, \tau, E) is a tt -soft \alpha T_2 -space, then there exist disjoint soft \alpha -open sets U_{i_E} and V_{i_E} such that x\in U_{i_E} and y\in V_{i_E} . Therefore \{V_{i_E}\} forms a soft \alpha -open cover of H_E . Since H_E is soft \alpha -compact, then H_E \subseteq\widetilde{\bigcup}_{i = 1}^{i = n}V_{i_E} . By letting \widetilde{\bigcup}_{i = 1}^{i = n}V_{i_E} = V_E and \widetilde{\bigcap}_{i = 1}^{i = n}U_{i_E} = U_E , we obtain the desired result.

    Theorem 3.39. Every soft \alpha -compact and tt -soft \alpha T_2 -space is tt -soft \alpha -regular.

    Proof. Let H_E be a soft \alpha -closed subset of soft \alpha -compact and tt -soft \alpha T_2 -space (X, \tau, E) such that x\not\Subset H_E . Then H_E is soft \alpha -compact. By Theorem (3.38), there exist disjoint soft \alpha -open sets U_E and V_E such that x\in U_E and H_E\subseteq V_E . Thus, (X, \tau, E) is tt -soft \alpha -regular.

    Corollary 3.40. Every soft \alpha -compact and tt -soft \alpha T_2 -space is tt -soft \alpha T_3 .

    Lemma 3.41. Let F_E be a soft \alpha -open subset of a soft \alpha -regular space. Then for each P^x_e\in F_E , there exists a soft \alpha -open set G_E such that P^x_e \in\overline{G_E}^{\alpha}\widetilde{\subseteq} F_E .

    Proof. Let F_E be a soft \alpha -open set such that P^x_e \in F_E . Then x\not\in F^c_E . Since (X, \tau, E) is soft \alpha -regular, then there exist two disjoint soft \alpha -open sets G_E and W_E containing x and F^c_E , respectively. Thus x\in G_E\widetilde{\subseteq} W^c_E\widetilde{\subseteq}F_E . Hence, P^x_e\in G_E\widetilde{\subseteq}\overline{G_E}^{\alpha} \widetilde{\subseteq}W^c_E\widetilde{\subseteq}F_E .

    Theorem 3.42. Let H_E be a soft \alpha -compact subset of a soft \alpha -regular space and F_E be a soft \alpha -open set containing H_E . Then there exists a soft \alpha -open set G_E such that H_E\widetilde{\subseteq}G_E \widetilde{\subseteq} \overline{G_E}^{\alpha}\widetilde{\subseteq}F_E .

    Proof. Let the given conditions be satisfied. Then for each P^x_e\in H_E , we have P^x_e\in F_E . Therefore there is a soft \alpha -open set W_{{xe}_E} such that P^x_e\in W_{{xe}_E} \widetilde{\subseteq}\overline{W_{{xe}_E}}^{\alpha}\widetilde{\subseteq} F_E . Now, \{W_{{xe}_E}:P^x_e\in F_E\} is a soft \alpha -open cover of H_E . Since H_E is soft \alpha -compact, then H_E\widetilde{\subseteq}\widetilde{\bigcup}_{i = 1}^{i = n}W_{{xe}_E} . Putting G_E = \widetilde{\bigcup}_{i = 1}^{i = n}W_{{xe}_E} . Thus H_E\widetilde{\subseteq}G_E \widetilde{\subseteq} \overline{G_E}^{\alpha}\widetilde{\subseteq}F_E .

    Corollary 3.43. If (X, \tau, E) is soft \alpha -compact and soft \alpha T_3 , then it is tt -soft \alpha T_4 .

    Proof. Suppose that F_{1_E} and F_{2_E} are two disjoint soft \alpha -closed sets. Then F_{2_E} \widetilde{\subseteq}F^c_{1_E} . Since (X, \tau, E) is soft \alpha -compact, then F_{2_E} is soft \alpha -compact and since (X, \tau, E) is soft \alpha -regular, then there is a soft \alpha -open set G_E such that F_{2_E}\widetilde{\subseteq}G_E \widetilde{\subseteq} \overline{G_E}^{\alpha}\widetilde{\subseteq}F^c_{1_E} . Obviously, F_{2_E}\widetilde{\subseteq}G_E, F_{1_E}\widetilde{\subseteq}(\overline{G_E}^{\alpha})^c and G_E\widetilde{\bigcap}(\overline{G_E}^{\alpha})^c = \widetilde{\Phi} . Thus (X, \tau, E) is soft \alpha -normal. Since (X, \tau, E) is soft \alpha T_3 , then it is tt -soft \alpha T_1 . Hence, it is tt -soft \alpha T_4 .

    In this section, we investigate main features of an \alpha -fixed soft point, in particular, those are related to parametric topological spaces.

    Theorem 4.1. Let \{\mathcal{B}_n: n\in\mathbb{N}\} be a collection of soft subsets of a soft \alpha -compact space (X, \tau, E) satisfying:

    (ⅰ) \mathcal{B}_n\neq\widetilde{\Phi} for each n\in\mathbb{N} ;

    (ⅱ) \mathcal{B}_n is a soft \alpha -closed set for each n\in\mathbb{N} ;

    (ⅲ) \mathcal{B}_{n+1}\widetilde{\subseteq}\mathcal{B}_{n} for each n\in\mathbb{N} .

    Then \widetilde{\bigcap}_{n\in \mathbb{N}}\mathcal{B}_{n}\neq \widetilde{\Phi} .

    Proof. Suppose that \widetilde{\bigcap}_{n\in \mathbb{N}}\mathcal{B}_{n} = \widetilde{\Phi} . Then \widetilde{\bigcup}_{n\in \mathbb{N}}\mathcal{B}^c_{n} = \widetilde{X} . It follows from (ii) that \{\mathcal{B}^c_n: n\in\mathbb{N}\} is a soft \alpha -open cover of \widetilde{X} . By hypothesis of soft \alpha -compactness, there exist i_1, i_2, ..., i_k\in \mathbb{N} , i_1 < i_2 < ... < i_k such that \widetilde{X} = \mathcal{B}^c_{i_1}\widetilde{\bigcup} \mathcal{B}^c_{i_2}\widetilde{\bigcup}... \widetilde{\bigcup}\mathcal{B}^c_{i_k} . It follows from (iii) that \mathcal{B}_{i_k}\widetilde{\subseteq}\widetilde{X} = \mathcal{B}^c_{i_1} \widetilde{\bigcup} \mathcal{B}^c_{i_2}\widetilde{\bigcup}... \widetilde{\bigcup}\mathcal{B}^c_{i_k} = [\mathcal{B}_{i_1}\widetilde{\bigcap} \mathcal{B}_{i_2}\widetilde{\bigcap}... \widetilde{\bigcap}\mathcal{B}_{i_k}]^c = \mathcal{B}^c_{i_k} . This yields a contradiction. Thus we obtain the proof that \widetilde{\bigcap}_{n\in \mathbb{N}}\mathcal{B}_{n}\neq \widetilde{\Phi} .

    To illustrate the above theorem, we give the following example

    Example 4.2. As we mentioned that a soft topological space is a classical topological space if E = \{e\} is a singleton. Then we show the above theorem in the crisp setting. Let \tau = \mathbb{R}\bigcup\{G\subseteq\mathbb{R}:1\not\in \mathbb{R}\} be a (soft) topology on \mathbb{R} (it is called an excluding point topology). One can examined that (\mathbb{R}, \tau, E) is a soft \alpha -compact space. Let \{\mathcal{M}_n: n\in\mathbb{N}\} be a collection of soft subsets of (\mathbb{R}, \tau, E) defined as follows: \mathcal{M}_n = \mathbb{N}\setminus\{2, ..., n+1\} ; that is \mathcal{M}_1 = \mathbb{N}\setminus\{2\} , \mathcal{M}_2 = \mathbb{N}\setminus\{2, 3\} , and so on. It is clear that \mathcal{M}_n satisfied the three conditions (i)-(iii) given in the above theorem. Now, 1\in \bigcap_{n\in \mathbb{N}}\mathcal{M}_{n} , as required.

    Proposition 4.3. Let (X, \tau, E) be a soft \alpha -compact and soft \alpha T'_2 -space and g_\varphi:(X, \tau, E)\rightarrow (X, \tau, E) be a soft \alpha^{\star} -continuous map. Then there exists a unique soft point P^x_e\in \widetilde{X} of g_\varphi .

    Proof. Let \{\mathcal{B}_1 = g_\varphi(\widetilde{X}) and \mathcal{B}_n = g_\varphi(\mathcal{B}_{n-1}) = g^n_\varphi(\widetilde{X}) for each n\in\mathbb{N}\} be a family of soft subsets of (X, \tau, E) . It is clear that \mathcal{B}_{n+1}\widetilde{\subseteq} \mathcal{B}_{n} for each n\in\mathbb{N} . Since g_\varphi is soft \alpha^{\star} -continuous, then \mathcal{B}_n is a soft \alpha -compact set for each n\in\mathbb{N} and since (X, \tau, E) is soft \alpha T'_2 , then \mathcal{B}_n is also a soft \alpha -closed set for each n\in\mathbb{N} . It follows from Theorem (4.1) that (H, E) = \widetilde{\bigcap}_{n\in\mathbb{N}} \mathcal{B}_n is a non null soft set. Note that g_\varphi(H, E) = g_\varphi(\widetilde{\bigcap}_{n\in\mathbb{N}}g^n_\varphi(\widetilde{X})) \widetilde{\subseteq} \widetilde{\bigcap}_{n\in\mathbb{N}}g^{n+1}_\varphi(\widetilde{X}) \widetilde{\subseteq} \widetilde{\bigcap}_{n\in\mathbb{N}}g^{n}_\varphi(\widetilde{X}) = (H, E) . To show that (H, E)\widetilde{\subseteq} g_\varphi(H, E) , suppose that there is a P^x_e\in (H, E) such that P^x_e\not\in g_\varphi(H, E) . Let \mathcal{C}_n = g^{-1}_\varphi(P^x_e)\widetilde{\bigcap} \mathcal{B}_n . Obviously, \mathcal{C}_n\neq\widetilde{\Phi} and \mathcal{C}_n\widetilde{\subseteq} \mathcal{C}_{n-1} for each n\in\mathbb{N} . By Theorem (2.15), \mathcal{C}_n is a soft \alpha -closed set for each n\in\mathbb{N} ; and by Theorem (4.1), there exists a soft point P^y_m such that P^y_m\in g^{-1}_\varphi(P^x_e) \widetilde{\bigcap} \mathcal{B}_n . Therefore P^x_e = g_\varphi(P^y_m)\in g_\varphi(H, E) . This is a contradiction. Thus, g_\varphi(H, E) = (H, E) . Hence, the proof is complete.

    Definition 4.4. (ⅰ) (X, \tau, E) is said to have an \alpha -fixed soft point property if every soft \alpha^{\star} -continuous map g_\varphi:(X, \tau, E)\rightarrow (X, \tau, E) has a fixed soft point.

    (ⅱ) A property is said to be an \alpha^{\star} -soft topological property if the property is preserved by soft \alpha^{\star} -homeomorphism maps.

    Proposition 4.5. The property of being an \alpha -fixed soft point is an \alpha^{\star} -soft topological property.

    Proof. Let (X, \tau, E) and (Y, \theta, E) be a soft \alpha^{\star} -homeomorphic. Then there is a bijective soft map f_\varphi:(X, \tau, E)\rightarrow (Y, \theta, E) such that f_\varphi and f^{-1}_\varphi are soft \alpha^{\star} -continuous. Since (X, \tau, E) has an \alpha -fixed soft point property, then every soft \alpha^{\star} -continuous map g_\varphi:(X, \tau, E)\rightarrow (X, \tau, E) has an \alpha -fixed soft point. Now, let h_\varphi:(Y, \theta, E)\rightarrow (Y, \theta, E) be a soft \alpha^{\star} -continuous. Obviously, h_\varphi\circ f_\varphi:(X, \tau, E)\rightarrow (Y, \theta, E) is a soft \alpha^{\star} -continuous. Also, f^{-1}_\varphi\circ h_\varphi\circ f_\varphi:(X, \tau, E)\rightarrow (X, \tau, E) is a soft \alpha^{\star} -continuous. Since (X, \tau, E) has an \alpha -fixed soft point property, then f^{-1}_\varphi(h_\varphi(f_\varphi(P^x_e))) = P^x_e for some P^x_e\in \widetilde{X} . consequently, f_\varphi(f^{-1}_\varphi(h_\varphi(f_\varphi(P^x_e)))) = f_\varphi(P^x_e) . This implies that h_\varphi(f_\varphi(P^x_e)) = f_\varphi(P^x_e) . Thus f_\varphi(P^x_e) is an \alpha -fixed soft point of h_\varphi . Hence, (Y, \theta, E) has an \alpha -fixed soft point property, as required.

    Before we investigate a relationship between soft topological space and their parametric topological spaces in terms of possessing a fixed (soft) point, we need to prove the following result.

    Theorem 4.6. Let \tau be an extended soft topology on X . Then a soft map g_{\varphi}:(X, \tau, E)\rightarrow (Y, \theta, E) is soft \alpha^{\star} -continuous if and only if a map g:(X, \tau_{e})\rightarrow (Y, \theta_{\phi(e)}) is \alpha^{\star} -continuous.

    Proof. Necessity: Let U be an \alpha -open subset of (Y, \theta_{\phi(e)}) . Then there exists a soft \alpha -open subset G_E of (Y, \theta, E) such that G(\phi(e)) = U . Since g_{\varphi} is a soft \alpha^{\star} -continuous map, then g^{-1}_{\phi}(G_E) is a soft \alpha -open set. From Definition (2.9), it follows that a soft subset g^{-1}_{\phi}(G_E) = (g^{-1}_{\phi}(G))_E of (X, \tau, E) is given by g^{-1}_{\phi}(G)(e) = g^{-1}(G(\phi(e))) for each e\in E . By hypothesis, \tau is an extended soft topology on X , we obtain from Theorem (2.26) that a subset g^{-1}(G(\phi(e))) = g^{-1}(U) of (X, \tau_{e}) is \alpha -open. Hence, a map g is \alpha^{\star} -continuous.

    Sufficiency: Let G_E be a soft \alpha -open subset of (Y, \theta, E) . Then from Definition (2.9), it follows that a soft subset g^{-1}_{\phi}(G_E) = (g^{-1}_{\phi}(G))_E of (X, \tau, E) is given by g^{-1}_{\phi}(G)(e) = g^{-1}(G(\phi(e))) for each e\in E . Since a map g is \alpha^{\star} -continuous, then a subset g^{-1}(G(\phi(e))) of (X, \tau_{e}) is \alpha -open. By hypothesis, \tau is an extended soft topology on X , we obtain from Theorem (2.26) that g^{-1}_{\phi}(G_E) is a soft \alpha -open subset of (X, \tau, E) . Hence, a soft map g_{\varphi} is soft \alpha^{\star} -continuous.

    Definition 4.7. (X, \tau) is said to have an \alpha -fixed point property if every \alpha^{\star} -continuous map g:(X, \tau)\rightarrow (X, \tau) has a fixed point.

    Proposition 4.8. (X, \tau, E) has the property of an \alpha -fixed soft point iff (X, \tau_{e}) has the property of an \alpha -fixed point for each e\in E .

    Proof. Necessity: Let (X, \tau, E) has the property of an \alpha -fixed soft point. Then every soft \alpha^{\star} -continuous map g_\varphi:(X, \tau, E)\rightarrow (X, \tau, E) has a fixed soft point. Say, P^x_e . It follows from the above theorem that g_e:(X, \tau_{e})\rightarrow (X, \theta_{\phi(e)}) is \alpha^{\star} -continuous. Since P^x_e is a fixed soft point of g_\varphi , then it must be that g_e(x) = x . Thus, g_e has a fixed point. Hence, we obtain the desired result.

    Sufficiency: Let (X, \tau_{e}) has the property of an \alpha -fixed point for each e\in E . Then every \alpha^{\star} -continuous map g_e:(X, \tau_{e})\rightarrow (X, \theta_{\phi(e)}) has a fixed point. Say, x . It follows from the above theorem that g_{\varphi}:(X, \tau, E)\rightarrow (X, \theta, E) is soft \alpha^{\star} -continuous. Since x is a fixed point of g_e , then it must be that g_{\varphi}(P^x_e) = P^x_e . Thus, g_{\varphi} has a fixed soft point. Hence, we obtain the desired result.

    This work presents new types of soft separation axioms with respect to three factors:

    (ⅰ) ordinary points.

    (ⅱ) total belong and total non-belong relations.

    (ⅲ) soft \alpha -open sets.

    We show the interrelationships between these soft separation axioms and investigate some properties. The main contributions of this work are the following:

    (ⅰ) formulate new soft separation axioms, namely tt -soft \alpha T_i (i = 0, 1, 2, 3, 4) and tt -soft \alpha -regular spaces.

    (ⅱ) illustrate the relationships between them as well as with soft \alpha T_i (i = 0, 1, 2, 3, 4) and soft \alpha -regular spaces.

    (ⅲ) study the "transmission" of these soft separation axioms between soft topological space and its parametric topological spaces.

    (ⅳ) give some conditions that guarantee the equivalence of tt -soft \alpha T_i (i = 0, 1, 2) and the equivalence of tt -soft \alpha T_i (i = 1, 2, 3) .

    (ⅴ) characterize some of these soft separation axioms such as tt -soft \alpha T_1 and tt -soft \alpha -regular spaces

    (ⅵ) explore the interrelations of some of these soft separation axioms and soft compact spaces.

    (ⅶ) discuss the behaviours of these soft separation axioms with some notions such as product soft spaces and sum of soft topological spaces.

    (ⅷ) define \alpha -fixed soft point and establish fundamental properties.

    Soft separation axioms are among the most widespread and important concepts in soft topology because they are utilized to classify the objects of study and to construct different families of soft topological spaces. In this work, we have introduced new soft separation axioms with respect to ordinary points by using total belong and total non-belong relations. This way of definition helps us to generalize existing comparable properties via general topology and to remove a strict condition of the shape of soft open and closed subsets of soft \alpha -regular spaces. In general, we study their main properties and illustrate the interrelations between them and some soft topological notions such as soft compactness, product soft spaces and sum of soft topological spaces. We complete this work by defining \alpha -fixed soft point theorem and investigating its basic properties.

    We plan in the upcoming works to study the concepts and results presented herein by using some celebrated types of generalizations of soft open sets such as soft preopen, soft b -open and soft \beta -open sets. In addition, we will explore these concepts on some contents such as supra soft topology and fuzzy soft topology. In the end, we hope that the concepts initiated herein will find their applications in many fields soon.

    The authors declare that they have no competing interests.

    The authors would like to thank the referees for their valuable comments which help us to improve the manuscript.



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