The Commutation of Finite Sets: a Challenging Problem

Authors:
Christian Choffrut;Juhani Karhumaki;Nicolas Ollinger
Affiliations:
-;-;-
Venue:
The Commutation of Finite Sets: a Challenging Problem
Year:
1999

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Abstract

We prove that given a set X of two nonempty words, a set Y of nonempty words commutes with X if and only if either Y is a union of powers of X or $X,Y\subseteq t^+$ for some primitive word t. We also show that the same holds for certain special types of codes, but does not hold in general for sets of cardinality at least four.