MULTI-PUSH-DOWN LANGUAGES AND GRAMMARS
Luca Breveglieri, Alessandra Cherubini, Claudio Citrini, Stefano Crespi Reghizzi · International Journal of Foundations of Computer Science · 1996
A new class of languages, called multi-push-down (mpd), that generalize the classical context-free (cf, or Chomsky type 2) ones is introduced. These languages preserve some important properties of cf languages: a generalization of the Chomsky-Schützenberger homomorphic characterization theorem, the Parikh theorem and a “pumping lemma” are proved. Multi-push-down languages are an AFL. Their recognizers are automata equipped with a multi-push-down tape. Multi-push-down languages form a hierarchy based on the number of push-down tapes.