Hello,

Could you please let me know what is wrong with the following proof:

proof that L = a*b* is not regular:Suppose L is regular, so the Pumping Lemma applies to L. Let p be the pumping constant for L.Consider w = a b^p ∈ L.

| w | ≥ p, so the pumping lemma applies to w.

Thus there exist x, y, z ∈ { a, b }* such that w = xyz and 1 ≤ | y | ≤ p.

Take y = abn (n ≤ p), so x = ε and z = bp-n.

Now w2 = x y^2 z = a b^n a b^p ∉ L.

This contradicts the Pumping Lemma and so L is not regular.