Ogden's Lemma for Context-Free Languages Proof

Here we give a proof of Ogden's Lemma, which is a generalization of the pumping lemma for context-free languages. It's the same general idea, except now we can arbitrarily mark a number of symbols in the string, and the decomposition of the string contains some number of marked symbols. This generalizes the usual pumping lemma because the usual PL has "marked" symbols as being all of the symbols in the string. But for Ogden's Lemma, we can have some unmarked characters.

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