In: Computer Science
Given the language L={w| the number of a’s is greater than or equal to the number of b’s in w}
a) Using the Pumping Lemma to prove L is not a regular language.
b) Using closure property to prove L is not a regular language.
Claim
1. L1 = {w ∈ {a,b}∗ : w has the same number of as and bs} is not
regular.
Proof. Note that L1 ∩ a∗b∗ = {aibi : i ≥ 0}. Now assume towards
contradiction that L1 is regular. Since a∗b∗ is regular, and
regular languages are closed under intersection, then the
intersection is also regular. But we know that {aibi : i ≥ 0} is
not regular – contradiction.