Subwords and Power-Free Words are not Expressible by Word Equations
Lucian Ionel Ilie · Fundamenta Informaticae · 1999
We consider several open problems of Karhumäki, Mignosi, and Plandowski, cf. [KMP], concerning the expressibility of languages and relations as solutions of word equations. We show first that the (scattered) subword relation is not expressible. Then,