Pushdown Automaton: CFL and the pumping lemma

From PDA to CFG
• For any word w accepted by a PDA
P=(Q,,,,q 0 ,q f ) the process starts at q 0 with an
empty stack and ends at q f with an empty stack.
• Definition: for any two states p,qQ we define
L p,q to be the language that if we starts at p with
an empty stack and run on wL p,q we end at q
with an empty stack.
• We define for L p,q a variables A p,q s.t.
L p,q = {w | A p,q * w}
• Note, that L(P)=L q0 ,q f
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