Say that a variable A in CFG G is necessary if it appears
Chapter , Problem 5.35(choose chapter or problem)
Say that a variable A in CFG G is necessary if it appears in every derivation of some string w G. Let NECESSARYCFG = {hG,Ai| A is a necessary variable in G}.a. Show that NECESSARYCFG is Turing-recognizable. b. Show that NECESSARYCFG is undecidable.
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