Hairpin lengthening and shortening of regular languages

Abstract

We consider here two formal operations on words inspired by the DNA biochemistry: hairpin lengthening introduced in [15] and its inverse called hairpin shortening. We study the closure of the class of regular languages under the non-iterated and iterated variants of the two operations. The main results are: although any finite number of applications of the hairpin lengthening to a regular language may lead to non-regular languages, the iterated hairpin lengthening of a regular language is always regular. As far as the hairpin shortening operation is concerned, the class of regular languages is closed under bounded and unbounded iterated hairpin shortening. © 2012 Springer-Verlag Berlin Heidelberg.