A Boolean algebra with few subalgebras, interval Boolean algebras and retractiveness

It is well known that the laws of logic governing the sentence connectives—“and”, “or”, “not”, etc.—can be expressed by means of equations in the theory of Boolean algebras. The task of providing a similar algebraic setting for the full first-order predicate logic is the primary concern of algebraic logicians. The best-known efforts in this direction are the polyadic algebras of Halmos (cf. [2]) and the cylindric algebras of Tarski (cf. [3]), both of which may be described as Boolean algebras with infinitely many additional operations. In particular, there is a primitive operator, cκ, corresponding to each quantification, ∃υκ. In this paper we explore a version of algebraic logic conceived by A. H. Copeland, Sr., and described in [1], which has this advantage: All operators are generated from a finite set of primitive operations.Following the theory of cylindric algebras, we introduce, in the natural way, the classes of Copeland set algebras (SCpA), representable Copeland algebras (RCpA), and Copeland algebras of formulas. Playing a central role in the discussion is the set, Γ, of all equations holding in every set algebra. The reason for this is that the operations in a set algebra reflect the notion of satisfaction of a formula in a model, and hence an equation expresses the fact that two formulas are satisfied by the same sequences of objects in the model. Thus to say that an equation holds in every set algebra is to assert that a certain pair of formulas are logically equivalent.

A monadic (Boolean) algebra is a Boolean algebra A together with an operator 3 on A (called an existential quantifier, or, simply, a quantifier) such that 30=0, pfk 3p, and 3(^A 3q) = 3p* 3g whenever p and q are in A. Most of this note uses nothing more profound about monadic algebras than the definition. The reader interested in the motivation for and the basic facts in the theory of monadic algebras may, however, wish to consult [2]. Every Boolean algebra can be converted into a monadic algebra, usually in several ways. (One way is to write 3p = p for all p; another is to write Bp =0 or 1 according p =0 or py^O. These special operators are known the discrete and the simple quantifier, respectively.) It follows, a fortiori, that every Boolean algebra can be embedded into a monadic algebra, and it is clear, on grounds of universal algebra, that among the monadic extensions of a Boolean algebra there is one that is as free possible. To be more precise, let us say that a monadic algebra A is a free monadic extension of a Boolean algebra B if (i) B is a Boolean subalgebra of A, (ii) A is (monadically) generated by B, (iii) every Boolean homomorphism g that maps B into an arbitrary monadic algebra C has a (necessarily unique) extension to a monadic homomorphism f that maps A into C. The statement that a monadic extension as free possible always exists means that every Boolean algebra B has a free monadic extension A; the algebra A is uniquely determined to within a monadic isomorphism that is equal to the identity on B. The purpose of what follows is to give a constructive proof of this fact, i.e., a proof that exhibits A by means of certain set-theoretic constructions based on B (instead of a structurally not very informative proof via equivalence classes of strings of symbols). A by-product of the proof is a rather satisfying insight into the structure of the (Stone) dual space of the free monadic extension. The theorem can (and will) be formulated in such a way to subsume the results of Hyman Bass [l ] on the cardinal number of finitely generated free monadic algebras. The idea of the construction is this. Step 1: form a free Boolean algebra generated by a copy of B. Step 2: adjoin the elements of that

Let κ be a regular cardinal, and let B be a subalgebra of an interval algebra of size κ. The existence of a chain or an antichain of size κ in ℬ is due to M. Rubin (see [7]). We show that if the density of B is countable, then the same conclusion holds without this assumption on κ. Next we also show that this is the best possible result by showing that it is consistent with 2ℵ0 = ℵω1 that there is a boolean algebra B of size ℵω1 such that length(B) = ℵω1 is not attained and the incomparability of B is less than ℵω1. Notice that B is a subalgebra of an interval algebra. For more on chains and antichains in boolean algebras see. e.g., [1] and [2].

Boolean contact algebras constitute a suitable algebraic theory for qualitative spatial reasoning. They are Boolean algebras with an additional contact relation grasping the topological aspect of spatial entities. In this paper we present a logic that combines propositional logic, relevance logic, and modal logic to reason about Boolean contact algebras. This is done in two steps. First, we use the relevance logic operators to obtain a logic suitable for Boolean algebras. Then we add modal operators that are based on the contact relation. In both cases we present axioms that are equivalent to requirement that every frame for the logic is indeed a Boolean algebra resp. Boolean contact algebra. We also provide a natural deduction system for this logic by defining introduction and eliminations rules for each logical operator. The system is shown to be sound. Furthermore, we sketch an implementation of the natural deduction system in the functional programming language and interactive theorem prover Coq.

The isolation of dimensions from a data matrix has been traditionally formulated in terms of an al gebraic or geometric model. Order analysis was de veloped as a method of multidimensional analysis and scaling based on the theory of Boolean algebra. The order analytic algorithm utilizes functions of the propositional calculus in lieu of eigenvalues and eigenvectors of the general linear model. Also, the graphic presentation of latent space in coordinates of the Euclidian space is paralleled in ordering- theoretic models by dendrograms of the test space. A conceptual outline of order analysis is presented, followed by an empirical comparison of factor and order analysis solutions of a sample data problem. Resulting factor and order analytic structures are evaluated in terms of meeting criteria of simple structure and correct reflection of broad cognitive categories. In addition, the relations of proximity and dominance are discussed from the perspectives of both Cartesian and Leibnitzian theories of di mensionality as pertaining to problems of multi variate analysis and scaling.

By limiting the range of the predicate variables in a second-order language, one may obtain restricted versions of second-order logic such as weak second-order logic or definable subset logic. In this note, we provide an infinitary strongly complete axiomatization for several systems of this kind having the range of the predicate variables as a parameter. The completeness argument uses simple techniques from the theory of Boolean algebras. This article is dedicated to our friend John N. Crossley on the occasion of his 86th birthday.

On an unsolved problem from the theory of Boolean algebras

The theory of Boolean contact algebras has been used to represent a region based theory of space. Some of the primitives of Boolean algebras are not well motivated in that context. One possible generalization is to drop the notion of complement, thereby weakening the algebraic structure from Boolean algebra to distributive lattice. The main goal of this paper is to investigate the representation theory of that weaker notion, i.e., whether it is still possible to represent each abstract algebra by a substructure of the regular closed sets of a suitable topological space with the standard Whiteheadean contact relation.

The research aims to analyze geodetic methods for determining the location of natural reserve areas and standardizing the obtained data. The object of the research is the standardization of geodetic data for determining the boundaries of natural reserve areas. Normative and legal documents related to the classification and determination of territories of natural reserve areas and the main geodetic methods used to determine the boundaries of such areas were analyzed in the article. The structure and description of the main geodetic methods for the practical implementation of work to determine the location of natural reserve areas, including geodetic measurements, global navigation, and remote sensing methods, were also discussed. In addition, a number of discrepancies were identified in the process of obtaining, storing, and reproducing geodetic data. Overall, the article contains important information about methods for determining the boundaries of natural reserve areas and how mathematical methods can be used to standardize geodetic data by formalizing it. The research showed that formalization of geodetic data can be done using mathematical methods such as mathematical logic, Boolean algebra, and category theory. The article proposes the use of mathematical methods of data formalization, such as mathematical logic, Boolean algebra, and category theory, to structure and standardize geodetic data. Analytical and graphical models for standardizing geodetic data for determining the boundaries of natural reserve areas were developed using mathematical methods of formalization such as mathematical logic, Boolean algebra, and category theory.

The theory of discriminator algebras and varieties has been investigated extensively, and provides us with a wealth of information and techniques applicable to specific examples of such algebras and varieties. Here we give several such examples for Boolea

For any Boolean algebra A, $ \mathfrak{a} (A) $ is the smallest cardinality of an infinite partition of unity in A. A tower in a Boolean algebra A is a subset X of A well-ordered by the Boolean ordering, with $ 1 \not\in X $ but with $ \sum X = 1.\quad \mathfrak{a} (A) $ is the smallest cardinality of a tower of A. Given a linearly ordered set L with first element, the interval algebra of L is the algebra of subsets of L generated by the half-open intervals [a, b). We prove that there is an atomless interval algebra A such that $ \mathfrak{a} (a) $ < $ \mathfrak{t} (A)$ .

Often, we assume that an action is permitted simply because it is not explicitly forbidden; or, similarly, that an action is forbidden simply because it is not explicitly permitted. This kind of assumptions appear, e.g., in autonomous computing systems where decisions must be taken in the presence of an incomplete set of norms regulating a particular scenario. Combining default and deontic reasoning over actions allows us to formally reason about such assumptions. With this in mind, we propose a logical formalism for default reasoning over a deontic action logic. The novelty of our approach is twofold. First, our formalism for default reasoning deals with actions and action operators, and it is based on the deontic action logic originally proposed by Segerberg. Second, inspired by Segerberg's approach, we use tools coming from the theory of Boolean Algebra. These tools allow us to extend Segerberg's algebraic completeness result to the setting of Default Logics.

By using the universality of the theory of irreflexive symmetric graphs the universality of the theory of Boolean algebras with the Hartig quantifier is shown. Let b be any Boolean algebra with infinitely many atoms. Then the theory of b with the Hartig quantifier is undecidable.

A classic result in the theory of Boolean algebras states that the dual space of the Boolean algebra of all subsets of a set U is homeomorphic to the Stone-Čech compactification of the discrete space U. It is shown in this chapter that the natural extension of this result to Boolean algebras with operators is false. In more detail, the analogue for Boolean algebras with operators of the Boolean algebra of subsets of a set U is the complex algebra \(\mathfrak{C}\mathfrak{m}(U)\) of a relational structure \(\mathfrak{U}\). It is shown that the dual space of \(\mathfrak{C}\mathfrak{m}(U)\) is not, in general, homeo-isomorphic to the Stone-Čech compactification of the structure \(\mathfrak{U}\) endowed with the discrete topology. However, a characterization of the dual space of the complex algebra \(\mathfrak{C}\mathfrak{m}(U)\) is given that may be viewed as a generalization of the Boolean result: the dual space of \(\mathfrak{C}\mathfrak{m}(U)\) is homeo-isomorphic to the Stone-Čech weak compactification of the discrete space \(\mathfrak{U}\). In fact, there is a lattice isomorphism between the lattice of equivalence classes of weak compactifications of the discrete space \(\mathfrak{U}\) and the lattice of subalgebras of the complex algebra \(\mathfrak{C}\mathfrak{m}(U)\) that contain all singleton subsets; and this lattice isomorphism maps the Stone-Čech weak compactification of \(\mathfrak{U}\) to the complex algebra \(\mathfrak{C}\mathfrak{m}(U)\) itself. If a relational structure is of finitary character, then the preceding result holds with the term “weak compactification” replaced by “compactification”. In particular, for Boolean algebras without operators we obtain the new result that there is an isomorphism from the lattice of equivalence classes of compactifications of a discrete space U to the lattice of subalgebras of the Boolean algebra of all subsets of U that contain the finite subsets of U. The arguments needed to establish these results are based upon a hybrid duality theory for homomorphisms that combines aspects of the algebraic and topological duality theories developed in Chapters 1 and 2 respectively.KeywordsWeak CompactificationFinite CharacterComplex AlgebraDiscrete TopologySubalgebrasThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

We analyze Zorn's Lemma and some of its consequences for Boolean algebras in a constructive setting. We show that Zorn's Lemma is persistent in the sense that, if it holds in the underlying set theory, in a properly stated form it continues to hold in all intuitionistic type theories of a certain natural kind. (Observe that the axiom of choice cannot be persistent in this sense since it implies the law of excluded middle.) We also establish the persistence of some familiar results in the theory of (complete) Boolean algebras—notably, the proposition that every complete Boolean algebra is an absolute subretract. This (almost) resolves a question of Banaschewski and Bhutani as to whether the Sikorski extension theorem for Boolean algebras is persistent.