Disambiguation between comment and CRLF.
Theorem: fail-comment-when-match-crlf
(defthm fail-comment-when-match-crlf (implies (and (tree-match-element-p tree (element-rulename *crlf*) *grammar*) (tree-terminatedp tree)) (mv-nth 0 (parse-comment (append (tree->string tree) rest-input)))))