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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The Pumping Lemma - background<br />
• The upper occurrence of R has a larger subtree<br />
<strong>and</strong> generates vxy.<br />
• The lower occurrence of R has a smaller<br />
subtree <strong>and</strong> generates only x.<br />
• Both subtrees are generated by <strong>the</strong> same<br />
variable R.<br />
• That means if we substitute one for <strong>the</strong> o<strong>the</strong>r we<br />
will still obtain valid parse trees.<br />
S<br />
R<br />
R<br />
u v x y z<br />
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