UGC-NET | UGC NET CS 2017 Jan – III | Question 63

Which of the following statements is false?
(A) Every context-sensitive language is recursive.
(B) The set of all languages that are not recursively enumerable is countable.
(C) The family of recursively enumerable languages is closed under union.
(D) The families of recursively enumerable and recursive languages are closed under reversal.

Answer: (B)
Explanation:

1. Every context-sensitive language is recursiveCorrect
2. The set of all languages that are not recursively enumerable is countable.Incorrect
3. The family of recursively enumerable languages is closed under union.Correct
4. The families of recursively enumerable and recursive languages are closed under reversal.Correct

For more information Refer:Recursive and Recursive Enumerable Languages
Option (B) is correct.
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