The non-abelian squares are not context-free
نویسنده
چکیده
Erd˝ os introduced the notion of abelian square in a 1961 paper [1]: Definition 1. A word w is an abelian square if there exist two words s and t such that w = st and t is a permutation of s. Maxime Crochemore asked if the language of non-abelian squares is context-free. In this note, we answer his question. Let Σ = {0, 1} be the alphabet in this context. Let L denote the language of all words that are not abelian squares over Σ. Our goal is to prove the following: Theorem 2. L is not context-free.
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عنوان ژورنال:
- CoRR
دوره abs/1110.4136 شماره
صفحات -
تاریخ انتشار 2011