%0 Generic %D 2003 %T On three variants of rewriting P systems %A Claudio Ferretti %A Giancarlo Mauri %A Gheorghe Paun %A Claudio Zandron %C Amsterdam (The Netherlands) %I Elsevier %K chomsky hierarchy %K Lindenmayer systems %K Membrane computing %K regulated rewriting %N 1 %P 201-215 %R 10.1016/S0304-3975(02)00581-9 %U http://www.ingentaconnect.com/content/els/03043975/2003/00000301/00000001/art00581 %V 301 %X We continue here the study of P systems with string objects processed by rewriting rules, by investigating some questions which are classic in formal language theory: leftmost derivation, conditional use of rules (permitting and forbidding conditions), relationships with language families in Chomsky and Lindenmayer hierarchies.