The number of clones determined by disjunctions of unary relations

We consider finitary relations (also known as crosses) that are definable via finite disjunctions of unary relations, i.e. subsets, taken from a fixed finite parameter set $\Gamma$. We prove that whenever $\Gamma$ contains at least one non-empty relation distinct from the full carrier set, there is a countably infinite number of polymorphism clones determined by relations that are disjunctively definable from $\Gamma$. Finally, we extend our result to finitely related polymorphism clones and countably infinite sets $\Gamma$.Comment: manuscript to be published in Theory of Computing System

Tractability in Constraint Satisfaction Problems: A Survey

International audienceEven though the Constraint Satisfaction Problem (CSP) is NP-complete, many tractable classes of CSP instances have been identified. After discussing different forms and uses of tractability, we describe some landmark tractable classes and survey recent theoretical results. Although we concentrate on the classical CSP, we also cover its important extensions to infinite domains and optimisation, as well as #CSP and QCSP

On the Scope of the Universal-Algebraic Approach to Constraint Satisfaction

The universal-algebraic approach has proved a powerful tool in the study of the complexity of CSPs. This approach has previously been applied to the study of CSPs with finite or (infinite) omega-categorical templates, and relies on two facts. The first is that in finite or omega-categorical structures A, a relation is primitive positive definable if and only if it is preserved by the polymorphisms of A. The second is that every finite or omega-categorical structure is homomorphically equivalent to a core structure. In this paper, we present generalizations of these facts to infinite structures that are not necessarily omega-categorical. (This abstract has been severely curtailed by the space constraints of arXiv -- please read the full abstract in the article.) Finally, we present applications of our general results to the description and analysis of the complexity of CSPs. In particular, we give general hardness criteria based on the absence of polymorphisms that depend on more than one argument, and we present a polymorphism-based description of those CSPs that are first-order definable (and therefore can be solved in polynomial time).Comment: Extended abstract appeared at 25th Symposium on Logic in Computer Science (LICS 2010). This version will appear in the LMCS special issue associated with LICS 201

On the relationship of maximal C-clones and maximal clones

A restricted version of the Galois connection between polymorphisms and invariants, called Pol−CInv, is studied, where the invariant relations are restricted to so-called clausal relations. In this context, the relationship of maximal C-clones and maximal clones is investigated. It is shown that, with the exception of one special case occurring for Boolean domains, maximal C-clones are never maximal clones.:1 Introduction 2 Preliminaries 3 Proof of the main theorem 3.1 Principle of proof 3.2 Bounded orders 3.3 Non-trivial congruences 3.4 Selfdual functions 3.5 Quasilinear functions 3.6 Functions preserving central and h-regular relations 4 Concluding remarks ReferencesWir untersuchen eine eingeschränkte Variante der Galoisverbindung zwischen Polymorphismen und invarianten Relationen, bezeichnet mit Pol−CInv, wobei die invarianten Relationen auf sogenannte klausale Relationen beschränkt werden. In diesem Zusammenhang wird die Beziehung zwischen maximalen C-Klonen und maximalen Klonen betrachtet. Es wird gezeigt, daß, mit Ausnahme eines Spezialfalles für Boolesche Grundmengen, maximale C-Klone niemals maximale Klone sind.:1 Introduction 2 Preliminaries 3 Proof of the main theorem 3.1 Principle of proof 3.2 Bounded orders 3.3 Non-trivial congruences 3.4 Selfdual functions 3.5 Quasilinear functions 3.6 Functions preserving central and h-regular relations 4 Concluding remarks Reference

On the relationship of maximal C-clones and maximal clones

A restricted version of the Galois connection between polymorphisms and invariants, called Pol−CInv, is studied, where the invariant relations are restricted to so-called clausal relations. In this context, the relationship of maximal C-clones and maximal clones is investigated. It is shown that, with the exception of one special case occurring for Boolean domains, maximal C-clones are never maximal clones.:1 Introduction 2 Preliminaries 3 Proof of the main theorem 3.1 Principle of proof 3.2 Bounded orders 3.3 Non-trivial congruences 3.4 Selfdual functions 3.5 Quasilinear functions 3.6 Functions preserving central and h-regular relations 4 Concluding remarks ReferencesWir untersuchen eine eingeschränkte Variante der Galoisverbindung zwischen Polymorphismen und invarianten Relationen, bezeichnet mit Pol−CInv, wobei die invarianten Relationen auf sogenannte klausale Relationen beschränkt werden. In diesem Zusammenhang wird die Beziehung zwischen maximalen C-Klonen und maximalen Klonen betrachtet. Es wird gezeigt, daß, mit Ausnahme eines Spezialfalles für Boolesche Grundmengen, maximale C-Klone niemals maximale Klone sind.:1 Introduction 2 Preliminaries 3 Proof of the main theorem 3.1 Principle of proof 3.2 Bounded orders 3.3 Non-trivial congruences 3.4 Selfdual functions 3.5 Quasilinear functions 3.6 Functions preserving central and h-regular relations 4 Concluding remarks Reference

Automatic Construction of Implicative Theories for Mathematical Domains

Implication is a logical connective corresponding to the rule of causality "if ... then ...". Implications allow one to organize knowledge of some field of application in an intuitive and convenient manner. This thesis explores possibilities of automatic construction of all valid implications (implicative theory) in a given field. As the main method for constructing implicative theories a robust active learning technique called Attribute Exploration was used. Attribute Exploration extracts knowledge from existing data and offers a possibility of refining this knowledge via providing counter-examples. In frames of the project implicative theories were constructed automatically for two mathematical domains: algebraic identities and parametrically expressible functions. This goal was achieved thanks both pragmatical approach of Attribute Exploration and discoveries in respective fields of application. The two diverse application fields favourably illustrate different possible usage patterns of Attribute Exploration for automatic construction of implicative theories