Module
CFL Pumping Lemma and Non-Context-Free Languages
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About
Pumping lemma for context-free languages (and Ogden’s lemma light optional). Classic non-CFLs (aⁿbⁿcⁿ, {ww}, equal counts of three symbols). Closure and non-closure properties of CFLs (union/concat/star yes; intersection/complement no). Intersection of CFL and regular is CFL.
Goal
Apply the CFL pumping lemma to prove non-context-freeness; use closure/non-closure to classify languages; explain the two-counter / nested-dependency barrier of a single stack.
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