Well quasi-orders and the shuffle closure of finite sets

Flavio d'Alessandro (1) , Gwenaël Richomme (2) , Stefano Varrichio (3)

1 Sapienza University of Rome - Dipartimento di Matematica "Guido Castelnuovo" [Roma I]
2 LaRIA - Laboratoire de Recherche en Informatique d'Amiens
3 DIPMAT - Dipartimento di Matematica [Roma II]

Given a set I of words, the set of all words obtained by the shuffle of (copies of) words of I is naturally provided with a partial order. In [FS05], the authors have opened the problem of the characterization of the finite sets I such that the order is a well quasi-order . In this paper we give an answer in the case when I consists of a single word w.

Mots clés: Formal languages; Well quasi-orders; Shuffle

Domaines: Mathématique discrète [cs.DM]

Flavio d'Alessandro, Gwenaël Richomme, Stefano Varrichio. Well quasi-orders and the shuffle closure of finite sets. Theoretical Computer Science, 2007, 377, pp.73-92. ⟨hal-00085839⟩