Chomsky Normal Form. The number of leaves of a binary tree of height n is at most 2 n . Let G be a CFG in Chomsky Normal Form for the language L. Let n be the number of variables in G. Then any string z in L of length more than 2 n satisfies the Pumping Lemma for CFLs: there is a decomposition z = uvwxy such that uviwxiy belongs to L for all i greater than or equal to 0.