Let L₁ is context free language and L₂ is a regular language which of the…

1999

Let L₁ is context free language and L₂ is a regular language which of the following is/are false

  1. A.

    L₁ − L₂ is not context free

  2. B.

    L₁ ∩ L₂ is context free

  3. C.

    ~L₁ is context free

  4. D.

    ~L₂ is regular

  5. E.

    A and C

Attempted by 6 students.

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Correct answer: E

Context-free languages (CFLs) are not closed under complement, so ~L₁ is false. CFL minus regular (L₁ - L₂) equals L₁ ∩ ~L₂, which is context free.

Thus A and C are false statements.

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