On a stronger reconstruction notion for monoids and clones

Motivated by reconstruction results by Rubin, we introduce a new reconstruction notion for permutation groups, transformation monoids and clones, called automatic action compatibility, which entails automatic homeomorphicity. We further give a characterization of automatic homeomorphicity for transformation monoids on arbitrary carriers with a dense group of invertibles having automatic homeomorphicity. We then show how to lift automatic action compatibility from groups to monoids and from monoids to clones under fairly weak assumptions. We finally employ these theorems to get automatic action compatibility results for monoids and clones over several well-known countable structures, including the strictly ordered rationals, the directed and undirected version of the random graph, the random tournament and bipartite graph, the generic strictly ordered set, and the directed and undirected versions of the universal homogeneous Henson graphs.Comment: 29 pp; Changes v1-->v2::typos corr.|L3.5+pf extended|Rem3.7 added|C. Pech found out that arg of L5.3-v1 solved Probl2-v1|L5.3, C5.4, Probl2 of v1 removed|C5.2, R5.4 new, contain parts of pf of L5.3-v1|L5.2-v1 is now L5.3,merged with concl of C5.4-v1,L5.3-v2 extends C5.4-v1|abstract, intro updated|ref[24] added|part of L5.3-v1 is L2.1(e)-v2, another part merged with pf of L5.2-v1 => L5.3-v

Relational Structure Theory: A Localisation Theory for Algebraic Structures

This thesis extends a localisation theory for finite algebras to certain classes of infinite structures. Based on ideas and constructions originally stemming from Tame Congruence Theory, algebras are studied via local restrictions of their relational counterpart (Relational Structure Theory). In this respect, first those subsets are identified that are suitable for such a localisation process, i. e. that are compatible with the relational clone structure of the counterpart of an algebra. It is then studied which properties of the global algebra can be transferred to its localisations, called neighbourhoods. Thereafter, it is discussed how this process can be reversed, leading to the concept of covers. These are collections of neighbourhoods that allow information retrieval about the global structure from knowledge about the local restrictions. Subsequently, covers are characterised in terms of a decomposition equation, and connections to categorical equivalences of algebras are explored. In the second half of the thesis, a refinement concept for covers is introduced in order to find optimal, non-refinable covers, eventually leading to practical algorithms for their determination. Finally, the text establishes further theoretical foundations, e. g. several irreducibility notions, in order to ensure existence of non-refinable covers via an intrinsic characterisation, and to prove under some conditions that they are uniquely determined in a canonical sense. At last, the applicability of the developed techniques is demonstrated using two clear expository examples.:1 Introduction 2 Preliminaries and Notation 2.1 Functions, operations and relations 2.2 Algebras and relational structures 2.3 Clones 3 Relational Structure Theory 3.1 Finding suitable subsets for localisation 3.2 Neighbourhoods 3.3 The restricted algebra A|U 3.4 Covers 3.5 Refinement 3.6 Irreducibility notions 3.7 Intrinsic description of non-refinable covers 3.8 Elaborated example 4 Problems and Prospects for Future Research Acknowledgements Index of Notation Index of Terms BibliographyDiese Dissertation erweitert eine Lokalisierungstheorie für endliche Algebren auf gewisse Klassen unendlicher Strukturen. Basierend auf Ideen und Konstruktionen, die ursprünglich der Tame Congruence Theory entstammen, werden Algebren über lokale Einschränkungen ihres relationalen Gegenstücks untersucht (Relationale Strukturtheorie). In diesem Zusammenhang werden zunächst diejenigen Teilmengen identifiziert, welche für einen solchen Lokalisierungsprozeß geeignet sind, d. h., die mit der Relationenklonstruktur auf dem Gegenstück einer Algebra kompatibel sind. Es wird dann untersucht, welche Eigenschaften der globalen Algebra auf ihre Lokalisierungen, genannt Umgebungen, übertragen werden können. Nachfolgend wird diskutiert, wie dieser Vorgang umgekehrt werden kann, was zum Begriff der Überdeckungen führt. Dies sind Systeme von Umgebungen, welche die Rückgewinnung von Informationen über die globale Struktur aus Kenntnis ihrer lokalen Einschränkungen erlauben. Sodann werden Überdeckungen durch eine Zerlegungsgleichung charakterisiert und Bezüge zu kategoriellen Äquivalenzen von Algebren hergestellt. In der zweiten Hälfte der Arbeit wird ein Verfeinerungsbegriff für Überdeckungen eingeführt, um optimale, nichtverfeinerbare Überdeckungen zu finden, was letztlich zu praktischen Algorithmen zu ihrer Bestimmung führt. Schließlich erarbeitet der Text weitere theoretische Grundlagen, beispielsweise mehrere Irreduzibilitätsbegriffe, um die Existenz nichtverfeinerbarer Überdeckungen vermöge einer intrinsischen Charakterisierung sicherzustellen und, unter gewissen Bedingungen, zu beweisen, daß sie in kanonischer Weise eindeutig bestimmt sind. Schlußendlich wird die Anwendbarkeit der entwickelten Methoden an zwei übersichtlichen Beispielen demonstriert.:1 Introduction 2 Preliminaries and Notation 2.1 Functions, operations and relations 2.2 Algebras and relational structures 2.3 Clones 3 Relational Structure Theory 3.1 Finding suitable subsets for localisation 3.2 Neighbourhoods 3.3 The restricted algebra A|U 3.4 Covers 3.5 Refinement 3.6 Irreducibility notions 3.7 Intrinsic description of non-refinable covers 3.8 Elaborated example 4 Problems and Prospects for Future Research Acknowledgements Index of Notation Index of Terms Bibliograph

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

Minimal clones with many majority operations

We present two minimal clones containing 26 and 78 majority operations respectively, more than any other previously known example.Comment: 11 page

Some Examples of Minimal Groupoids on a Finite Set (Algebraic System, Logic, Language and Related Areas in Computer Science)

A minimal clone is an atom in the lattice of clones. The classification of minimal clones on a finite set still remains unsolved. A minimal groupoid is a minimal clone generated by a binary idempotent function. In this paper we report some examples of minimal groupoids generated by binary functions which resemble projections

On when the union of two algebraic sets is algebraic

In universal algebraic geometry, an algebra is called an equational domain if the union of two algebraic sets is algebraic. We characterize equational domains, with respect to polynomial equations, inside congruence permutable varieties, and with respect to term equations, among all algebras of size two and all algebras of size three with a cyclic automorphism. Furthermore, for each size at least three, we prove that, modulo term equivalence, there is a continuum of equational domains of that size.Comment: 50 pages, 1 figure, 1 tabl

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