CD Grammar Systems with Two Propagating Scattered Context Components Characterize the Family of Context Sensitive Languages
نویسندگان
چکیده
Are propagating scattered context grammars as powerful as context sensitive grammars? This question customarily referred to as the L (PSCG) = L (CS) (see [4]) problem, represents a long standing open problem in formal language theory. The present paper reformulates and answers this question in terms of CD grammar systems. More precisely, the paper introduces CD grammar systems whose components are propagating scattered context grammars. Then, it demonstrates that two-component grammar systems of this kind generate the family of context-sensitive languages, thus the answer to this problem is in affirmation if the problem is reformulated in the above way.
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Leftmost Derivations of Propagating Scattered Context Grammars: A New Proof
Propagating scattered context grammars, introduced in [3], represent an important type of semi-parallel rewriting systems. Since their introduction, however, the exact relationship of the family of languages they generate to the family of context-sensitive languages is unknown. The language family generated by these grammars is included in the family of context-sensitive languages; on the other...
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