We describe an intersection of the family of expressible relations and another natural family of relations. This is the first result of this kind existing in the literature. To obtain it we extend a tool for proving nonexpressibility of languages to a tool for proving nonexpressibility of relations.
2
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
We consider several open problems of Karhumäki, Mignosi and Plandowski, cf. [KMP], con-cerning the expressibility of languages and relations as solutions of word equations. We show first that the (scattered) subword relation is not expressible. Then, we consider the set of k-power-free finite words and solve it negatively for all nontrivial integer values of k. Finally, we consider the Fibonacci finite words. We do not solve the problem of the expressibility of the set of these words but prove that a negative answer (as believed) cannot be given using the tools in [KMP].
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.