Semi-commutations and rational expressions

Abstract

We extend the notion of concurrent iteration defined on trace languages by E. Oehmanski to languages closed under a semi-commutation relation which is the non-symmetric version of partial commutation relation: we iterate strongly connected components of words. For a given semi-commutation relation, this leads to the definition of a new family of rational languages closed under the semi-commutation. We give a necessary and sufficient condition for a language closed under a semi-commutation relation to be a rational language and we proved that the equality between the families of rational languages and recognizable languages closed under a semi-commutation relation is true if and only if the semi-commutation is symmetric (i. e a partial commutation).