Literally idempotent languages and their varieties - two letter case

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Authors	KLÍMA Ondřej POLÁK Libor
Year of publication	2010
Type	Article in Periodical
Magazine / Source	International Journal of Foundations of Computer Science
MU Faculty or unit	Faculty of Science
Citation
Field	General mathematics
Keywords	varieties of regular languages; idempotent semigroups; syntactic monoids
Description	We already studied classes of literally idempotent languages closely related to the (positive) varieties of the famous Straubing- Thérien hierarchy. In the present paper we start a systematic study of literal varieties of literally idempotent languages, namely we deal with the case of two letter alphabet. First, we consider natural canonical expressions for such languages. Secondly, we describe all possible classes of the form V ({a, b}) where V is a literal variety of literally idempotent languages.
Related projects:	Institute for Theoretical Computer Science Mathematical structures and their physical applications Algebraic Methods in Automata and Formal Language Theory II