Commutative images of rational languages and the Abelian kernel of a monoid

Issue		RAIRO-Theor. Inf. Appl. Volume 35, Number 5, September-October 2001


Page(s)		419 - 435
DOI		10.1051/ita:2001100

DOI: 10.1051/ita:2001100

Theoret. Informatics Appl. 35, 419-435 (2001)

Commutative images of rational languages and the Abelian kernel of a monoid

Manuel Delgado

Centro de Matemática, Universidade do Porto P. Gomes Teixeira, 4099-002 Porto, Portugal; mdelgado@fc.up.pt.

(Received March 6, 2001. Accepted March 1, 2002.)

Abstract
Natural algorithms to compute rational expressions for recognizable languages, even those which work well in practice, may produce very long expressions. So, aiming towards the computation of the commutative image of a recognizable language, one should avoid passing through an expression produced this way. We modify here one of those algorithms in order to compute directly a semilinear expression for the commutative image of a recognizable language. We also give a second modification of the algorithm which allows the direct computation of the closure in the profinite topology of the commutative image. As an application, we give a modification of an algorithm for computing the Abelian kernel of a finite monoid obtained by the author in 1998 which is much more efficient in practice.

Mathematics Subject Classification. 20M35, 68Q99

Key words: Rational language -- semilinear set -- profinite topology -- finite monoid.

© EDP Sciences 2001

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