Question: (30 points) Say that a variable A in CFG G is necessary if it appears in every derivation of some string wEL(G). Let NECESSARYcP(G, A)

(30 points) Say that a variable A in CFG G is necessary if it appears in every derivation of some string wEL(G). Let NECESSARYcP(G, A) A is a necessary variable in G (a) Show that NECESSARYCFG is Turing-recognizable. (b) Show that NECESSARY cPG is undecidable
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