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3.   These languages are not regular.   For each, list three strings that would work in a...

3.   These languages are not regular.   For each, list three strings that would work in a Pumping

Lemma proof.   Then, use one of them to show the language is not regular. But not a.

a.    L = {ww | w Î {a, b}*}

b.    L = {anba2n | n >= 0}

c.     {w Î S* | w contains more a’s than b’s}.

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Answer #1

a)L = {ww | w Î {a, b}*

Assume L is regular. From the pumping lemma there exists an n such that every w Î L such that |w| >=n can be represented as x y z with |y| not =0 and |xy| <= n. Let us choose an bn an bn . Its length is 4n >= n. Since the length of xy cannot exceed n, y must be of the form a for some k > 0. From the pumping lemma an+1bnanbnmust also be in L but it is not of the right form since the middle of the string would be in the middle of the b which prevents a match with the beginning of the string. Hence the language is not regular.

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