Context-free membership and emptiness
A finite context-free grammar has decidable membership: convert to Chomsky normal form and enumerate bounded derivations for a nonempty input word.
Key knowledge
A finite context-free grammar has decidable membership: convert to Chomsky normal form and enumerate bounded derivations for a nonempty input word. Emptiness is decided by repeatedly marking variables whose productions use only terminals or already productive variables; the language is nonempty iff the start variable is marked.
Conditions and scope
- Treat epsilon membership separately; an empty production is productive.
- Membership decidability does not imply that equivalence or ambiguity of arbitrary grammars is decidable.
Sources · 1
References
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Evidence and review
Lecture 7 slides 7–9, bounded CNF derivation and productive-variable fixed point; conversion proof referenced rather than independently certified.
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Entry details
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