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Structure of partially ordered cyclic semigroups

Józef Drewniak, Jolanta Sobera (2003)

Czechoslovak Mathematical Journal

This paper recalls some properties of a cyclic semigroup and examines cyclic subsemigroups in a finite ordered semigroup. We prove that a partially ordered cyclic semigroup has a spiral structure which leads to a separation of three classes of such semigroups. The cardinality of the order relation is also estimated. Some results concern semigroups with a lattice order.

Subtraction semigroups

Bohdan Zelinka (1995)

Mathematica Bohemica

A subtraction semigroup is a semigroup ( A , . , - ) with a further operation " - " added, called subtraction and satisfying certain axioms. The paper concerns a problem by B. M. Schein concerning the structure of multiplication in a subtraction semigroup.

The globals of pseudovarieties of ordered semigroups containing B 2 and an application to a problem proposed by Pin

Jorge Almeida, Ana P. Escada (2005)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

Given a basis of pseudoidentities for a pseudovariety of ordered semigroups containing the 5-element aperiodic Brandt semigroup B 2 , under the natural order, it is shown that the same basis, over the most general graph over which it can be read, defines the global. This is used to show that the global of the pseudovariety of level 3 / 2 of Straubing-Thérien’s concatenation hierarchy has infinite vertex rank.

The globals of pseudovarieties of ordered semigroups containing B2 and an application to a problem proposed by Pin

Jorge Almeida, Ana P. Escada (2010)

RAIRO - Theoretical Informatics and Applications

Given a basis of pseudoidentities for a pseudovariety of ordered semigroups containing the 5-element aperiodic Brandt semigroup B2, under the natural order, it is shown that the same basis, over the most general graph over which it can be read, defines the global. This is used to show that the global of the pseudovariety of level 3/2 of Straubing-Thérien's concatenation hierarchy has infinite vertex rank.

Currently displaying 301 – 320 of 366