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Let L1 be a recursive language. Let L2 and L3 be languages that are recursively enumerable but not recursive. Which of the following statements is not necessarily true?
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- L2 - L1 is recursively enumerable
- L1 - L3 is recursively enumerable
- L2 ∩ L1 is recursively enumerable
- L2 ∪ L1 is recursively enumerable
- L2 - L1 is recursively enumerable
Correct Option: B
L1 → recursive
L2 ,L3 → recursively enumerable but not recursive.
So L1 can be recursive enumerable.
RE - RE = RE
So L1 - L3 is recursively enumerable.
