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Monoid presentations of groups by finite special string-rewriting systems

Duncan W. Parkes, V. Yu. Shavrukov, Richard M. Thomas (2004)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

We show that the class of groups which have monoid presentations by means of finite special [ λ ] -confluent string-rewriting systems strictly contains the class of plain groups (the groups which are free products of a finitely generated free group and finitely many finite groups), and that any group which has an infinite cyclic central subgroup can be presented by such a string-rewriting system if and only if it is the direct product of an infinite cyclic group and a finite cyclic group.

Monoid presentations of groups by finite special string-rewriting systems

Duncan W. Parkes, V. Yu. Shavrukov, Richard M. Thomas (2010)

RAIRO - Theoretical Informatics and Applications

We show that the class of groups which have monoid presentations by means of finite special [λ]-confluent string-rewriting systems strictly contains the class of plain groups (the groups which are free products of a finitely generated free group and finitely many finite groups), and that any group which has an infinite cyclic central subgroup can be presented by such a string-rewriting system if and only if it is the direct product of an infinite cyclic group and a finite cyclic group.

Monotone (co)inductive types and positive fixed-point types

Ralph Matthes (2010)

RAIRO - Theoretical Informatics and Applications

We study five extensions of the polymorphically typed lambda-calculus (system F) by type constructs intended to model fixed-points of monotone operators. Building on work by Geuvers concerning the relation between term rewrite systems for least pre-fixed-points and greatest post-fixed-points of positive type schemes (i.e., non-nested positive inductive and coinductive types) and so-called retract types, we show that there are reduction-preserving embeddings even between systems of monotone (co)inductive...

More on the complexity of cover graphs

Jaroslav Nešetřil, Vojtěch Rödl (1995)

Commentationes Mathematicae Universitatis Carolinae

In response to [3] and [4] we prove that the recognition of cover graphs of finite posets is an NP-hard problem.

Morphismes sturmiens et règles de Rauzy

Filippo Mignosi, Patrice Séébold (1993)

Journal de théorie des nombres de Bordeaux

Nous donnons une caractérisation complète de tous les morphismes binaires qui préservent les mots sturmiens et montrons que les mots infinis engendrés par ces morphismes sont rigides.

Morphisms fixing words associated with exchange of three intervals

Petr Ambrož, Zuzana Masáková, Edita Pelantová (2010)

RAIRO - Theoretical Informatics and Applications

We consider words coding exchange of three intervals with permutation (3,2,1), here called 3iet words. Recently, a characterization of substitution invariant 3iet words was provided. We study the opposite question: what are the morphisms fixing a 3iet word? We reveal a narrow connection of such morphisms and morphisms fixing Sturmian words using the new notion of amicability.

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