Duality in Computer Science

Stone duality, topological algebra, and recognition

В цифровую эпоху в процессе автоматизации, роботизации различных отраслей производства и внедрения в него искусственного интеллекта используется уже трудно обозримое множество языков программирования. В результате в подготовке будущих инженеров все большое значение приобретает теория формальных языков, лежащая в основе разработки языков программирования. Незнание теории формальных языков стало причиной многих ошибок в разработке и использовании языков программирования в высокотехнологичных отраслях производства. Поэтому необходимо внедрение в содержание подготовки будущих инженеров дисциплины «Элементы теории формальных языков» для овладения ими теорией и практикой языков программирования. Установлено, что в методической литературе не разработаны эффективные методы обучения будущих инженеров формальным языкам. Цель статьи заключается в исследовании важных математических и методических аспектов обучения теории формальных языков будущих инженеров. Ведущую роль в исследовании играли методология дискретной математики и абстрактной алгебры, культурологический подход и методика преемственности в обучения между школой и вузом в содержании подготовки будущих инженеров. Результаты исследования. Охарактеризована культурологическая роль дискретной математики в современной теории формальных языков. На основе анализа избранных трудов В. М. Глушкова, Д. Кнута и других ученых исследована фундаментальная роль формальных языков абстрактной алгебры в обучении теории формальных языков. Охарактеризованы алгебраические аспекты методики обучения теории формальных языков и грамматик и роль в этой методике классических понятий абстрактной алгебры и их свойств. На основе этого изложены элементы методики преемственности в обучении элементам теории формальных языков будущих инженеров. В этих элементах важную роль играют различные трактовки понятия «язык» и примеры языков из математики и информатики. Раскрыта важная роль грамматик формальных языков в дальнейшем обучении этой теории. Результаты статьи имеют важное теоретическое и практическое значение в дальнейшем исследовании проблем методологии обучения будущих инженеров элементам теории формальных языков. Они представляют интерес для преподавателей, ведущих профессиональную подготовку студентов инженерных направлений в сфере автоматизации, роботизации отраслей производства и внедрения в него Искусственного интеллекта. In the digital era, in the process of automation, robotization of various industries and the introduction of Artificial Intelligence into it, numerous programming languages are widely applied. As a result, the theory of formal languages ​that underlies the development of programming languages is becoming increasingly important in the training of engineering students. The nescience of formal languages theory has caused many mistakes in the development and use of programming languages ​in high-tech industries. Therefore, it is necessary to introduce the discipline "Elements of the Theory of Formal Languages" into the content of the training of future engineers in order to master the theory and practice of programming languages. At the same time, it was established that the methodological literature hasn’t developed effective methods for teaching future engineers to formal languages. The purpose of the article is to investigate important mathematical and methodological aspects of teaching the theory of formal languages ​to engineering students. The leading role in the study was played by the methodology of discrete math and abstract algebra. Also, the cultural approach and the methodology of pre-graduation in training between school and university in the content of training future engineers. Findings.The cultural role of discrete mathematics in the modern theory of formal languages is determined in the article. Based on the analysis of selected works of V.M. Glushkov, D. Knut, and other scientists, the article investigates the fundamental role of formal languages ​of abstract algebra in teaching the theory of formal languages. Algebraic aspects of teaching methodology of the theory of formal languages ​and grammars, and the role in this methodology of classical concepts of abstract algebra and their propertieshave also become the subjects of the study. Basing on this, the elements of the methodology of continuity in teaching the elements of the theory of formal languages of future engineers are set out in the article. Various interpretations of the concept of "language" and examples of languages from mathematics, and computer science play an important role in these elements. The research also states the important role of grammars of formal languages in the further training of this theory. The findings of the research have important theoretical and practical significance in the further study of the issues of the methodology for teaching future engineers to the elements of the theory of formal languages. They are of interest to teachers conducting the professional training of engineering students in the field of automation, robotization of production industries, and the introduction of Artificial Intelligence into it.

We extend the theory of profinite algebras, as it is used in the algebraic theory of regular languages, to the more general setting of Stone topological algebras with the ultimate goal of going beyond classes of regular languages. We introduce Stone pseudovarieties, that is, classes of Stone topological algebras of a fixed topological signature that are closed under taking Stone quotients, closed subalgebras and finite direct products. Looking at the dual Stone spaces of Boolean algebras of subsets of a given topological algebra, we find a simple characterization of when the dual space admits a natural structure of topological algebra; the characterization is given in terms of how the Boolean algebra behaves under the inverses of the operation evaluation mappings of each arity. This provides an alternative, which is presented in the form of an equivalence of categories, to the duality theory of M. Gehrke. As an application, a Stone quotient of a Stone topological algebra that is residually in a given Stone pseudovariety is shown to be also residually in it, thereby extending the corresponding result of M. Gehrke for the Stone pseudovariety of all finite algebras over discrete signatures, which was recently extended to topological signatures jointly by the authors and H. Goulet-Ouellet. The residual closure of a Stone pseudovariety is thus a Stone pseudovariety, and these are precisely the Stone analogues of varieties. A Birkhoff type theorem for Stone varieties is also established and it is shown how Reiterman’s theorem can be derived from it.

The motivation for this paper comes from the following sources. First, one can observe that the two major concepts underlying the methods of reasoning with incomplete information are the concept of degree of truth of a piece of information and the concept of approximation of a set of information items. We shall refer to the theories employing the concept of degree of truth as to theories of fuzziness and to the theories employing the concept of approximation as to theories of roughness (see [6] for a survey). The algebraic structures relevant to these theories are residuated lattices ([7], [12], [13], [16], [17], [18], [22], [23]) and Boolean algebras with operators ([19], [21], [10], [11]), respectively. Residuated lattices provide an arithmetic of degrees of truth and Boolean algebras equipped with the appropriate operators provide a method of reasoning with approximately determined information. Both classes of algebras have a lattice structure as a basis. Second, both theories of fuzziness and theories of roughness develop generalizations of relation algebras to algebras of fuzzy relations [20] and algebras of rough relations ([4], [5], [9]), respectively. In both classes a lattice structure is a basis. Third, not necessarily distributive lattices with modal operators, which can be viewed as most elementary approximation operators, are recently developed in [24] (distributive lattices with operators are considered in [14] and [25]). With this background, our aim is to begin a systematic study of the classes of algebras that have the structure of a (not necessarily distributive) lattice and, moreover, in each class there are some operators added to the lattice which are relevant for binary relations. Our main interest is in developing relational representation theorems for the classes of lattices with operators under consideration. More precisely, we wish to guarantee that each algebra of our classes is isomorphic to an algebra of binary relations on a set. We prove the theorems of that form by suitably extending the Urquhart representation theorem for lattices ([26]) and the representation theorems presented in [1]. The classes defined in the paper are the parts which put together lead to what might be called lattice-based relation algebras. Our view is that these algebras would be the weakest structures relevant for binary relations. All the other algebras of binary relations considered in the literature would then be their signature and/or axiomatic extensions.Throughout the paper we use the same symbol for denoting an algebra or a relational system and their universes.KeywordsBinary RelationDistributive LatticeRepresentation TheoremResiduated LatticeRelation AlgebraThese 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.

Stone duality relates logic, in the form of Boolean algebra, to spaces. Stone-type dualities abound in computer science and have been of great use in understanding the relationship between computational models and the languages used to reason about them. Recent work on probabilistic processes has established a Stone-type duality for a restricted class of Markov processes. The dual category was a new notion---Aumann algebras---which are Boolean algebras equipped with countable family of modalities indexed by rational probabilities. In this article we consider an alternative definition of Aumann algebra that leads to dual adjunction for Markov processes that is a duality for many measurable spaces occurring in practice. This extends a duality for measurable spaces due to Sikorski. In particular, we do not require that the probabilistic modalities preserve a distinguished base of clopen sets, nor that morphisms of Markov processes do so. The extra generality allows us to give a perspicuous definition of event bisimulation on Aumann algebras.

We introduce a meta-model based on formal languages, dubbed formal choreographic languages, to study message-passing systems. Our framework allows us to generalise standard constructions from the literature and to compare them. In particular, we consider notions such as global view, local view, and projections from the former to the latter. The correctness of local views projected from global views is characterised in terms of a closure property. We consider a number of communication properties -- such as (dead)lock-freedom -- and give conditions on formal choreographic languages to guarantee them. Finally, we show how formal choreographic languages can capture existing formalisms; specifically we consider communicating finite-state machines, choreography automata, and multiparty session types. Notably, formal choreographic languages, differently from most approaches in the literature, can naturally model systems exhibiting non-regular behaviour.

The Dual Complexity Space as the Dual of a Normed Cone

Written for graduate students and advanced undergraduates in computer science, A Second Course in Formal Languages and Automata Theory treats topics in the theory of computation not usually covered in a first course. After a review of basic concepts, the book covers combinatorics on words, regular languages, context-free languages, parsing and recognition, Turing machines, and other language classes. Many topics often absent from other textbooks, such as repetitions in words, state complexity, the interchange lemma, 2DPDAs, and the incompressibility method, are covered here. The author places particular emphasis on the resources needed to represent certain languages. The book also includes a diverse collection of more than 200 exercises, suggestions for term projects, and research problems that remain open.

An algebraic approach to the theory of regular languages of finite and infinite words (∞-languages) is presented. It extends the algebraic theory of regular languages of finite words, which is based on finite semigroups. Their role is taken over by a structure called right binoid. A variety theorem is proved: there is a one-to-one correspondence between varieties of ∞-languages and pseudovarieties of right binoids. The class of locally threshold testable languages and several natural subclasses (such as the class of locally testable languages) as well as classes of the Borel hierarchy over the Cantor space (restricted to regular languages) are investigated as examples for varieties of ∞-languages. The corresponding pseudovarieties of right binoids are characterized and in some cases defining equations are derived. The connections with the algebraic description and classification of regular languages of infinite words in terms of finite semigroups are pointed out.

For any Boolean space X and a discrete almost distributive lattice D, it is proved that the set C(X, D) of all continuous mappings of X into D, when D is equipped with the discrete topology, is an almost Boolean algebra under pointwise operations. Conversely, it is proved that any almost Boolean algebra is a homomorphic image of C(X,D) for a suitable Boolean space X and a discrete almost distributive lattice D.

It is well known that in a distributive lattice L, every filter is an intersection of prime filters, and dually. Moreover, L is relatively complemented if and only if every prime filter (ideal) is maximal. In 1947, A. Monteiro [3] posed the question of determining whether a distributive lattice, in which every filter is an intersection of maximal filters, and dually, is necessarily relatively complemented. This question also appears as Problem 39 in G. Gr/itzer [2; p. 156]. Monteiro states that J. Dieudonn6 and L. Nachbin have independently shown that neither the condition that every filter is an intersection of maximal filters, nor its dual, implies the other. We will solve this problem in the negative by constructing a non-Boolean distributive lattice L which satisfies the above conditions on the filters and ideals L. The referee was most helpful in simplifying the explanation of the construction of L. This lattice is necessarily infinite for if a finite distributive lattice is such that each of its filters is an intersection of maximal filters then it is a Boolean algebra. Indeed, this follows from the fact that if F, F1,..., F, are prime filters and F = Of="1 Fi then F=Fto for some io~ {1,..., n}.

Engaging and maintaining student engagement with the content of a course in formal language theory and the theory of computation is notoriously difficult. A major factor is student's perception of the relevance of the required mathematical material to computer science as they have studied the discipline. Usually, the mathematical material discourages students and for many it forms an insurmountable barrier. This paper describes the construction of a course using the discovery learning technique known as the Moore Method that directly addresses student engagement with this material. The results of the delivery of this course were that students remained engaged with the course throughout the semester and enthusiastically received the pedagogical approach employed. While the course described was delivered to a small class in a liberal arts college, it may be adapted to larger class sizes and taught in any computer science program.

Traditionally, formal languages are defined as sets of words. More recently, the alternative coalgebraic or coinductive representation as infinite tries, i.e., prefix trees branching over the alphabet, has been used to obtain compact and elegant proofs of classic results in language theory. In this article, we study this representation in the Isabelle proof assistant. We define regular operations on infinite tries and prove the axioms of Kleene algebra for those operations. Thereby, we exercise corecursion and coinduction and confirm the coinductive view being profitable in formalizations, as it improves over the set-of-words view with respect to proof automation.

We introduce geometric consideration into the theory of formal languages. We aim to shed light on our understanding of global patterns that occur on infinite strings. We utilise methods of geometric group theory. Our emphasis is on large scale geometries. Two infinite strings have the same large scale geometry if there are colour preserving bi-Lipschitz maps with distortions between the strings. Call these maps quasi-isometries. Introduction of large scale geometries poses several questions. The first question asks to study the partial order induced by quasi-isometries. This partial order compares large scale geometries; as such it presents an algebraic tool for classification of global patterns. We prove there is a greatest large scale geometry and infinitely many minimal large scale geometries. The second question is related to understanding the quasi-isometric maps on various classes of strings. The third question investigates the sets of large scale geometries of strings accepted by computational models, e.g. Buchi automata. We provide an algorithm that describes large scale geometries of strings accepted by Buchi automata. This links large scale geometries with automata theory. The fourth question studies the complexity of the quasi-isometry problem. We show the problem is Σ 3 0-complete thus providing a bridge with computability theory. Finally, the fifth question asks to build algebraic structures that are invariants of large scale geometries. We invoke asymptotic cones, a key concept in geometric group theory, defined via model-theoretic notion of ultra-product. Partly, we study asymptotic cones of algorithmically random strings thus connecting the topic with algorithmic randomness.

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.