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Which of the following languages below are NOT recursively enumerable ?

L1 = {<M> / M is a TM that accepts all even numbers }.

L2 = {<M> / M does not accept all even numbers }

L3 = {<M> / M rejects all even numbers }

A) Only L1

B) Only L1 and L2

C) Only L1 and L

D) All of L1,L2 and L

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2 Answers

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answer is D

because all are UNDECIDABLE ..

so, UNDECIDABLE languages are always NOT RE laguages
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ANS (A)

0 IS AN EVEN NUMBER NOT ACCEPTED BY TM SINCE TM CANNOT ACCEPT EPSILLON

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