First induction step of the completeness lemma for parse-option.
Theorem:
(defthm parse-option-when-tree-match-induction-step-1 (implies (and (not (mv-nth 0 (parse-ichar #\[ input))) (mv-nth 0 (parse-alternation (mv-nth 2 (parse-*cwsp (mv-nth 2 (parse-ichar #\[ input)))))) (pred-alternation (mv-nth 2 (parse-*cwsp (mv-nth 2 (parse-ichar #\[ input)))))) (pred-option input)))