Disambiguation between "0" and "1".
Theorem: fail-0-when-match-1
(defthm fail-0-when-match-1 (implies (tree-match-element-p tree (element-char-val (char-val-insensitive nil "1")) *grammar*) (mv-nth 0 (parse-ichar #\0 (append (tree->string tree) rest-input)))))