效绵鼎 Proof of Lemma 1 If all paths in the parse tree of a CNF grammar are of length m+1,then the longest yield has length 2m-1,as in: m variables one terminal 2m-1 terminals 6Proof of Lemma 1 ◼ If all paths in the parse tree of a CNF grammar are of length < m+1, then the longest yield has length 2 m-1 , as in: 6 m variables one terminal 2 m-1 terminals