Discussion
A useless nonterminal in a grammar is one that
Answer: A
Correct answer: derives no terminal string or is unreachable from the start symbol
Either fault makes the nonterminal contribute nothing to the language: one that derives no terminal string can never complete a derivation, and one unreachable from the start symbol can never begin one. Both are removed before parsing, since they only complicate the tables and can mask genuine errors in the grammar.
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