Document Type

Technical Report

Publication Date

Summer 8-1-1973


Given a rewriting system G (its alphabet, the set of productions and the axiom) one can define the language of G by (i) taking out of all stings generated by G only those which are over a distinguished subalphabet of G, or (ii) translating the set of all strings generated by G by a fixed homomorphism. The "trade-offs" between these two mechanisms for defining languages are discussed for both, "parallel" rewriting systems from developmental systems hierarchy and "sequential" rewriting systems from the Chomsky hierarchy.