Input decomposition theorem for parse-*wsp/vchar.
Theorem: input-decomposition-of-parse-*wsp/vchar
(defthm input-decomposition-of-parse-*wsp/vchar (b* (((mv & trees rest-input) (parse-*wsp/vchar input))) (equal (append (tree-list->string trees) rest-input) (nat-list-fix input))))