Showing papers on "Indexed language published in 1970"

Full AFLs and nested iterated substitution

Abstract: A superAFL is a family of languages closed under union with unitary sets, intersection with regular sets, and nested iterated substitution and containing at least one nonunitary set Every superAFL is a full AFL containing all context-free languages If L is a full principal AFL, then Ŝ∞(L), the least superAFL containing L, is full principal If L is not substitution closed, the substitution closure of L is properly contained in Ŝ∞(L) The indexed languages form a superAFL which is not the least superAFL containing the one-way stack languages If L has a decidable emptiness problem, so does Ŝ∞(L) IfDs is an AFA, L = L(Ds) and Dw is the family of machines whose data structure is a pushdown store of tapes of Ds, then L(Ds) = Ŝ∞(L) if, and only if, Ds is nontrivial If Ds is uniformly erasable and L(Ds) has a decidable emptiness problem, then it is decidable if a member of Dw is finitely nested

Tree-oriented proofs of some theorems on context-free and indexed languages

Abstract: In this paper we study some applications and generalizations of the yield theorem: the yield of a recognizable set of trees (dendrolanguage) is an indexed language [1]. Standard results on context-free languages can be obtained quickly using this theorem. We consider here the Peters-Ritchie theorem [4]: the language analyzable by a finite set of CS rules is CF. An extension of the yield theorem reads: the yield of a CF set of trees is an indexed language. We prove some closure properties of CF sets of trees. Applying the yield theorem, we obtain properties of indexed languages. As a special result, we can solve the infiniteness problem for such languages.