On Pattern Expression Languages
Cezar Câmpeanu, Nicolae Sântean · 2006
Abstract. In this paper we show that the family of pattern expression languages is closed under the intersection with regular languages. Since this family is not closed under complement but is closed under reverse, a natural question arises, that is, whether particular languages such as those containing words of type ww R are pattern expression languages or not. We give a proof for a negative answer to this question, and we provide several examples of languages which can not be specified by pattern expressions. 1