Gate2020 cs Q32

0. Consider the following sentences.
I. If L1 ⋃ L2 is regular, then both L1 and L2 must be regular.
II. The class of regular languages is closed under infinite union.
Which of the above statements is/are TRUE?

  • Option : B
  • Explanation :
    Let L1 = an bn⇒ CFL
    L2 = Σ* ⇒ Regular
    L1 ∪ L2 = (an bn) ∪ Σ* = Σ* ⇒ Regular
    Since L1 ∪ L2 is regular but L1 is not regular, Hence statement I is false.
    Regular language is not closed under infinite union.
    Hence, statement-II is also false.
    ∴ Neither I nor II is true.
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