Let \(L_1 \), \(L_2 \) be two regular languages and \(L_3 \)a language which…

2024

Let \(L_1 \), \(L_2 \) be two regular languages and \(L_3 \)a language which is not regular. Which of the following statements is/are always TRUE?

  1. A.

    \(L_1 = L_2 \) if and only if \( {L_1 \cap \overline{L_2}} = \text{𝜙}\)

  2. B.

    𝐿1 ∪ 𝐿3 is not regular

  3. C.

    \(\overline{L_3}\) is not regular

  4. D.

    \(\overline{L_1} ∪ \overline{L_2}\) is regular

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Correct answer: C, D

Correct statements:

  • The complement of L3 is not regular.

    Reason: Regular languages are closed under complement. If complement(L3) were regular, then L3 would be the complement of a regular language and thus regular, contradicting the hypothesis that L3 is not regular.

  • The union of complement(L1) and complement(L2) is regular.

    Reason: L1 and L2 are regular, so complement(L1) and complement(L2) are regular (closure under complement). The union of two regular languages is regular (closure under union), so complement(L1) ∪ complement(L2) is regular.

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