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تسجيل مستخدم جديدPermutations of context-free and indexed languages
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We consider the cyclic closure of a language, and its generalisation to the operators $C^k$ introduced by Brandstadt. We prove that the cyclic closure of an indexed language is indexed, and that if $L$ is a context-free language then $C^k(L)$ is indexed.
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We study the links between the topological complexity of an omega context free language and its degree of ambiguity. In particular, using known facts from classical descriptive set theory, we prove that non Borel omega context free languages which ar
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