Separating some splicing models

In this paper we show that the three main definitions of the splicing opera tion known in the literature, i.e., the Head [Bull. Math. Biology 49 (1987) 737-759], Paun [Theoret. Comput. Sci. 168 (1996) 321-326] and Pixton [Disc rete Appl. Math. 69 (1996) 101-124] definitions, give rise to different sub classes of regular languages, when a finite set of rules is iterated on a f inite set of axioms. More precisely, we show that the family of regular lan guages generated by finite splicing, as defined in the early paper by Head, is strictly included in the family defined later by Paun, which is in turn strictly included in the splicing family defined by Pixton. We describe in stance languages in the difference sets, and we prove that they cannot be g enerated by the smaller families. (C) 2001 Elsevier Science B.V. All rights reserved.