Which of the following are correct for regular expressions? a. ∅ + L = L + ∅ = L b. εL = Lε = L c. ∅L = L∅ = ∅ d. ∅L = L∅ = L

1. Aa, b and d only
2. Ba, b and c only
3. Cb and d only
4. Da and d only

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Show answer & explanation

Correct answer: B. a, b and c only

Explanation

∅ is the identity for union and the annihilator for concatenation; ε is the identity for concatenation. So a, b and c are correct and d is false.