4 Semigroups and Monoids

4.1 Finitely Presented Semigroups

  • Construction of fp-semigroups and monoids

  • Direct product, free product

  • Arithmetic (free reduction on words only)

  • Definition of ideals and subsemigroups

  • Tietze transformations

4.2 Monoids Defined by Rewrite Systems

This is a category of finitely presented monoids where the relations are interpreted as rewrite rules. The most important case is that in which the monoid is defined by a confluent system of rewrite rules. A monoid of this category is typically constructed by applying the Knuth-Bendix procedure to a finitely presented monoid. Magma uses the Knuth-Bendix developed by Derek Holt in his package kbmag.

  • Construction of an RWS monoid from an fp-monoid using the Knuth-Bendix procedure. Orderings supported include: RT-recursive, recursive, ShortLex, WT-ShortLex and Wreath

  • Test a rewrite system for confluence

  • Reduction of a word to normal form

  • Operations on words: Product, exponentiation, equality

  • Test for a monoid being finite

  • Enumeration of elements

  • Definition of homomorphisms whose domain or codomain is an RWS monoid