Useless rules

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In formal grammar, useless rules are rules of symbol production which are unreachable or unproductive, that is, they are rules of production which can never be applied.

[edit] Cleaning Useless Rules

[edit] Examples

S \to Bb | Cc

B \to Bb | b

C \to Cc | c

D \to Bd | Cd

D is unreachable.

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