Pumping Lemma and Ogden Lemma for Displacement Context-Free Grammars
نویسنده
چکیده
The pumping lemma and Ogden lemma offer a powerful method to prove that a particular language is not context-free. In 2008 Kanazawa proved an analogue of pumping lemma for well-nested multiplecontext free languages. However, the statement of lemma is too weak for practical usage. We prove a stronger variant of pumping lemma and an analogue of Ogden lemma for the class of tree-adjoining languages. We also use these statements to prove that some natural context-sensitive languages cannot be generated by tree-adjoining grammars.
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