In formal language theory, a context-free grammar (CFG) is a grammar in which every production rule is of the formV → w where V is a single nonterminal symbol, and w is a string of terminals and/or nonterminals (possibly empty). The term "context-free" expresses the fact that nonterminals can be rewritten without regard to the context in which they occur. A formal language is context-free if some context-free grammar generates it.
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