International Journal of Mathematics and Mathematical Sciences

Volume 2012 (2012), Article ID 259541, 8 pages

http://dx.doi.org/10.1155/2012/259541

## A Comparison of Implications in Orthomodular Quantum Logic—Morphological Analysis of Quantum Logic

Department of Systems Design and Informatics, Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Iizuka-shi 820-8502, Japan

Received 26 June 2012; Accepted 3 August 2012

Academic Editor: Shigeru Kanemitsu

Copyright © 2012 Mitsuhiko Fujio. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

Morphological operators are generalized to lattices as adjunction pairs (Serra, 1984; Ronse, 1990; Heijmans and Ronse, 1990; Heijmans, 1994). In particular, morphology for set lattices is applied to analyze logics through Kripke semantics (Bloch, 2002; Fujio and Bloch, 2004; Fujio, 2006). For example, a pair of morphological operators as an adjunction gives rise to a temporalization of normal modal logic (Fujio and Bloch, 2004; Fujio, 2006). Also, constructions of models for intuitionistic logic or linear logics can be described in terms of morphological interior and/or closure operators (Fujio and Bloch, 2004). This shows that morphological analysis can be applied to various non-classical logics. On the other hand, quantum logics are algebraically formalized as orhomodular or modular ortho-complemented lattices (Birkhoff and von Neumann, 1936; Maeda, 1980; Chiara and Giuntini, 2002), and shown to allow Kripke semantics (Chiara and Giuntini, 2002). This suggests the possibility of morphological analysis for quantum logics. In this article, to show an efficiency of morphological analysis for quantum logic, we consider the implication problem in quantum logics (Chiara and Giuntini, 2002). We will give a comparison of the 5 polynomial implication connectives available in quantum logics.

#### 1. Mathematical Morphology

Mathematical morphology is a method of non-linear signal processing using simple set-theoretic operations, which has the feasibility of extracting the characteristic properties of shapes [1, 2]. In this paper we will adopt the formulation thereof generalized on lattices [3–7].

We identify a binary relation and the correspondence from to . Namely, for . We call the relation with and exchanged, the *transpose* of and denote it by .

##### 1.1. Dilation and Erosion

Let , be partially ordered sets. If for any family of which has a supremum in , the image has the supremum in and holds, then we call the mapping a *dilation* from to . Similarly, by changing supremum by infimum, we may introduce an *erosion*. We call dilation and erosion *morphological operations*. For two elements of , we have , , the morphological operations are monotone.

*Example 1.1 (morphology of set lattices [7]). * Given sets and , consider the lattices of their power sets , . Let be a binary relation in . Then the mappings and defined by
are a dilation and an erosion, respectively.

From the transpose we may similarly define the dilation and erosion , .

The importance of this example lies in the fact that all morphological operations between set lattices are expressed in this form, whence it follows that giving a framework of morphological operations and a binary relation are equivalent. In particular, in the Kripke semantics, accessibility relationships being binary operations between possible worlds, we contend that giving the Kripke framework amounts to giving morphological operations.

##### 1.2. Adjunctions

Suppose two mappings and between partially ordered sets satisfy the condition for any , . Then the mapping pair is called an adjunction and is written as and is called the lower adjoint of , with is the upper adjoint of . Notice that every adjoint is uniquely determined if exists.

Proposition 1.2. *For two monotone mappings and between partially ordered sets to satisfy , it is necessary and sufficient that for any , , the relation
**
holds. *

Relations between morphological operations and adjunctions are given by the following.

Proposition 1.3. *Let , be partially ordered sets and , . *(1)If has the upper adjoint, then it is a dilation. Conversely, if is a complete upper semilattice, then a dilation has the upper adjoint. (2)If has the lower adjoint, then it is an erosion. Conversely, if is a complete lower semilattice, then a dilation has the lower adjoint.

*Example 1.4 (adjunctions of set lattices [7]). * In Example 1.1, we have and . Note that in each adjunction pair, dilation and erosion, and are to be interchanged.

##### 1.3. Interior and Closure Operators

An idempotent monotone mapping on a partially ordered set is called a filter mapping. A *filter mapping* with extensibility () is called a *closure operator* and one with antiextensibility () is called an *interior operator*.

Proposition 1.5. *Let , be partially ordered sets and , and . Then is a closure operator of and is an interior operator of . *

*Example 1.6 (closing and opening). * The closure operator and the interior operator on which are induced by the adjunctions in Example 1.4 are called *closing* and *opening* by , respectively. Similarly, we may define the closing and opening by as operators on .

In any complete lattice, closure operators are characterized by the notion of Moore family [8], where a *Moore family* is a subset of a partially ordered set which satisfies the following condition. For any subset , if has the infimum in , then holds true.

Proposition 1.7 (see [7, 8]). *Let be a partially ordered set. *(1)For any closure operator , the totality of all -closed sets forms a Moore family.(2)If is a complete lattice, then for any Moore family , there exists a unique closure operator on such that holds.

We may establish similar properties of interior operators by appealing to the duality of a Moore family [7].

#### 2. Quantum Logic

We refer to [9, 10] for quantum logic and lattice theory associated to it and we assemble here the minimum requisites for the subsequent discussions.

For simplicity’s sake, we assume that the lattice always has the maximum element and the minimum element throughout in what follows.

##### 2.1. OL and OQL

An *ortho-complemented lattice * is a lattice which has an involutive and complementary operation reversing the order:(1), .(2).(3).

If, moreover, for and its complement , the modular relation
holds, then is called an *orthomodular lattice*.

An ortho-complemented lattice satisfying the modular relation for any , is an orthomodular, but not conversely. A Boolean lattice is an ortho-complemented lattice satisfying the modular relation. The inclusion order among these classes of lattices is

In general, we call collectively *quantum logic* (*QL*) both *orthologic* (*OL*) modelled on an ortho-complemented lattice and *orthomodular logic* (*OQL*) modelled on an orthomodular lattice. An orthomodular lattice being an ortho-complemented lattice, we mostly work with OL, with additional mentioning of some special features intrinsic of OQL.

The language of QL consists of a countable number of propositional variables , and logical connectives (negation), (conjunction). Denote by the formulae with their totality. The disjunction is defined as an abbreviation of .

##### 2.2. Kripke Semantics

The pair of the set of all possible worlds and the reflexive and accessibility relations is called a *Kripke frame* or *orthogonal frame* of OL. Intuitionally, the binary relation means that and are “not orthogonal". Indeed, defining by , then we see that the reflexiveness corresponds to , while symmetry to .

For any set of possible worlds , we define its ortho-complement set by Then in view of this, the power set lattice of becomes ortho-complemented. The orthogonality of a set and the possible worlds is defined by Expressing the orthogonality in terms of morphological operations

In an orthogonal frame , we consider a special class of subsets called *propositions* in , that is, is a proposition in means that holds. As we shall see below, it immediately follows from the definition that formulae in OL may be interpreted by assigning propositions in an orthogonal frame.

Proposition 2.1. *In an orthogonal frame , for to be a proposition, it is necessary and sufficient that it is an -closed set () in the sense of morphology.**(Note that being symmetric, we have .) *

*Proof. *By (2.6), we have , whence

Corollary 2.2. *The totality of all propositions of forms a lower semi-complete ortho-complemented sublattice of . *

*Proof. *Note that , and that from reflexibility of , we have , so that , . Hence, , . Since is a Moore family, and *a fortiori* lower semi-complete. Also, since , we have for , , whence we obtain . Hence, is closed with respect to the complementation .

Let be a lower semi-complete ortho-complemented sub-lattice of and let be a mapping such that (1)(2). We call the set a *Kripke model* of OL, consisting of both this and the Kriplke frame .

If holds true, we write and say that the formula is true in the possible world . We call the formula such that is true in the model and write . More generally, if for any belonging to a set of formulae, we have , then we say that is a consequence of in the model and write . If further, these hold true in any models, then we say that they are logically true in or logical consequences of, OL respectively.

The Kripke semantics of the orthomodular logic OQL may be defined by considering as only those satisfying the orthomodular condition

#### 3. Morphological Analysis of Implication Connectives

##### 3.1. Implication Problem in QL

In quantum logic QL, the implication problem is important [10]. Not only those in quantum logic, but in general, an implication connective is required to satisfy, for any model , at least the conditions(1),(2)If and , then .

In QL, this condition may be stated as follows. For any Kripke model , we have Thus, we take (3.1) as a requirement for an implication connective in QL [10]. Then we note that the forumula in classical logic is not an implication connective in the sense of QL.

On the other hand, there are several candidates for implication connectives. However, there are only 5 polynomial ones in the sense that they are expressed in finitely many , , [10]: (i),(ii),(iii),(iv),(v).

These are the all candidates for polynomial implications in the free orthomodular lattice generated by two elements satisfying There is a distinction between OL and OQL in that they are really implications in the respective logic.

Theorem 3.1 (see [10]). *The polynomial implications are all implications in OQL but none of them are so in OL. *

*Proof. *Proof depends on the fact that for (3.1) to hold for each , it is necessary and sufficient that satisfies the orthomodular condition (2.8). For details we refer to [10].

Theorem 3.2. *In OQL, are logical consequences of , that is, in any Kripke model , we have
*

*Proof. *We fix a Kripke model . Interpretation of each implication is as follows, where we denote the interpretations of the formulae , by , , respectively. , , , , .*Proof of **.* It suffices to prove , which reads in morphological operations,
Taking complements of bothsides, we obtain
by the definition of dilation. Then by adjunction, this is equivalent to the following:
The last equality follows from the duality between and . However, this inclusion relation is always true.*Proof of *. It suffices to prove , which can be done as in the proof of .*Proof of *. , or what amounts to the same thing, it is enough to show . Further for this to be true, it is necessary and sufficient that , which is true, being equivalent to .*Proof of *. Enough to prove and the proof can be done in the same way as the proof of .

#### 4. Conclusion

By applying morphological analysis to a Kripke model in quantum logics, we have shown that is the strongest among the 5 polynomial implication connectives in OQL. Once one sees the result, one may feel that one could do without morphological analysis. However, the point lies in whether by just looking at the defining equation ((i)(v)) or its interpretation, one could recognize the conclusion. Thus, the merit of morphological analysis seems to be its intuitive lucidness as “Calculus.”

We would like to return to the analysis of connectives other than .

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