Technical Report CS0047

Title: Theory of w-languages; Part II a Study of Various Models of w-type Generation And Recognition
Authors: Rina S.Cohen and Arie Y. Gold
Abstract: w-languages are sets consisting of w-length strings; w-automata are recognition devices for w-languages. In a previous papee the basic notions of w-grammars, w-context-free languages (w-CFL's) and w-pushdown automata (w-PDA's) were first defined and studied. In this paper various modes of w-type generation are introduced and the effect of certain restrictions on the derivations in w-grammars is investigated. Several distinct models of recognition in w-PDA's are considered, giving rise to a hierarchy of subfamilies of the w-CFL's. The relations among these su~families are established and characterizations for each family are dertved. Non-leftmost derivations in w-CFG's are studied and it is shown that l~ftmost generation in w-CFG's is strictly more powerful than non-leftmost generation.
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