Third induction step of the completeness lemma for parse-element.
Theorem:
(defthm parse-element-when-tree-match-induction-step-3 (implies (and (mv-nth 0 (parse-rulename input)) (mv-nth 0 (parse-group input)) (mv-nth 0 (parse-option input)) (mv-nth 0 (parse-char-val input)) (not (mv-nth 0 (parse-num-val input))) (pred-group input) (pred-option input)) (pred-element input)))