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Is this language contextfree? {w1w2 | w1,w2 $\in$ {a,b}* $\land$ |w1| = |w2| $\land$ w1 $\neq$ w2}. I think it's not but can't prove it.

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marked as duplicate by Hendrik Jan, Apass.Jack, David Richerby, rici, Community Dec 9 '18 at 17:12

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