Notes on pre-set pushdown automata
Motivated by practical implementation-methods for recursive program-schemata we will define and study presetting techniques for push-down automata. The main results will characterize the languages of preset pda's in terms of types of iterated substitution languages. In particular when conditions of "locally finiteness" and of "finite returning" are imposed we get a feasible machine-model for a class of developmental languages. The accepted family extends to the smallest AFL enclosing it when we drop the condition of locally finiteness. At the same time this family will be the smallest such full AFL. If all conditions are removed, present pda's exactly represent the family of iterated regular substitution languages, a sub-family of the indexed languages. Deterministic preset pda's are also studied, and the language-family they define is shown to be closed under complementation, generalizing a classical result.
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