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In formal language theory, the Chomsky–Schützenberger representation theorem is a theorem derived by Noam Chomsky and Marcel-Paul Schützenberger about representing a given context-free language in terms of two simpler languages. These two simpler languages, namely a regular language and a Dyck language, are combined by means of an intersection and a homomorphism. A few notions from formal language theory are in order. A context-free language is ''regular'', if can be described by a regular expression, or, equivalently, if it is accepted by a finite automaton. A homomorphism is based on a function which maps symbols from an alphabet to words over another alphabet ; If the domain of this function is extended to words over in the natural way, by letting for all words and , this yields a ''homomorphism'' . A ''matched alphabet'' is an alphabet with two equal-sized sets; it is convenient to think of it as a set of parentheses types, where contains the opening parenthesis symbols, whereas the symbols in contains the closing parenthesis symbols. For a matched alphabet , the ''Dyck language'' is given by : words that are well-nested parentheses over . :Chomsky–Schützenberger theorem. A language ''L'' over the alphabet is context-free if and only if there exists : * a matched alphabet : * a regular language over , : * and a homomorphism :such that . Proofs of this theorem are found in several textbooks, e.g. or . ==References== * * 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Chomsky–Schützenberger representation theorem」の詳細全文を読む スポンサード リンク
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