Right Type Departmental Bulletin Paper

Abstract. We first survey some results concerning the generative power of $\mathrm{P} $ sys-tems with objects described by strings processed by rewriting and by splicing, then we consider $\mathrm{P} $ systems with multisets of string-objects processed by replication, splitting, point mutation, and crossover. A combination of these variants (systems with multisets of string-objects processed by rewriting and crossing-over, without using priorities) is shown to characterize the recursively enumerable languages (moreover, systems with five membranes suffice)..