效绵县 Back to the Proof of the Pumping Lemma Now we know that the parse tree for z has a path with at least m+1 variables. Consider some longest path. There are only m different variables,so among the lowest m+1 we can find two nodes with the same label,say A. The parse tree thus looks like: 7Back to the Proof of the Pumping Lemma ◼ Now we know that the parse tree for z has a path with at least m+1 variables. ◼ Consider some longest path. ◼ There are only m different variables, so among the lowest m+1 we can find two nodes with the same label, say A. ◼ The parse tree thus looks like: 7