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Ambiguous grammar
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=== An unambiguous grammar with multiple derivations === The existence of multiple derivations of the same string does not suffice to indicate that the grammar is ambiguous; only multiple ''leftmost'' derivations (or, equivalently, multiple parse trees) indicate ambiguity. For example, the simple grammar S β A + A A β 0 | 1 is an unambiguous grammar for the language { 0+0, 0+1, 1+0, 1+1 }. While each of these four strings has only one leftmost derivation, it has two different derivations, for example S [[Context-free grammar#Rule application|β]] A + A β 0 + A β 0 + 0 and S β A + A β A + 0 β 0 + 0 Only the former derivation is a leftmost one.
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