Which of the following is/are undecidable?
- First is Emptiness for CFG; whether a CFG is empty or not, this problem is decidable.
- Second is everything for CFG; whether a CFG will generate all possible strings (completeness of CFG), this problem is undecidable.
- Third is Regularity for REC; whether language generated by TM is regular is undecidable.
- Fourth is equivalence for regular; whether language generated by DFA and NFA are same is decidable.
Second and third will be undecidable. Hence, option (D) is Correct.
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