Context-free grammar

In formal language theory, a context-free grammar (CFG) is a formal grammar in which every production rule is of the form

$A\ \to\ \alpha$

where $A$ is a single nonterminal symbol, and $\alpha$ is a string of terminals and/or nonterminals ( $\alpha$ can be empty). A formal grammar is considered "context free" when its production rules can be applied regardless of the context of a nonterminal. No matter which symbols surround it, the single nonterminal on the left hand side can always be replaced by the right hand side. This is what distinguishes it from a context-sensitive grammar.

单词	Context Free Grammar
释义	Context Free Grammar 英语百科 Context-free grammar In formal language theory, a context-free grammar (CFG) is a formal grammar in which every production rule is of the form $A\ \to\ \alpha$ where $A$ is a single nonterminal symbol, and $\alpha$ is a string of terminals and/or nonterminals ( $\alpha$ can be empty). A formal grammar is considered "context free" when its production rules can be applied regardless of the context of a nonterminal. No matter which symbols surround it, the single nonterminal on the left hand side can always be replaced by the right hand side. This is what distinguishes it from a context-sensitive grammar.
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Context Free Grammar

Context-free grammar