Pushdown Automaton: CFL and the pumping lemma
Pushdown Automaton: CFL and the pumping lemma
Pushdown Automaton: CFL and the pumping lemma
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Non context-free Languages<br />
• Consider <strong>the</strong> language L={a i b i c i |i0}.<br />
• When trying to build a push-down automaton<br />
that recognizes L, we can compare <strong>the</strong> number<br />
of a-'s with b-'s or c-'s but not both;<br />
• If we compared <strong>the</strong> number of a-'s to <strong>the</strong><br />
number of b-'s <strong>the</strong>n we can't compare c-'s with<br />
any of <strong>the</strong>m, as at this stage <strong>the</strong> stack (or<br />
counter) is empty.<br />
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