;;;; -- L'esprit de l'escalier ------------------------------------------------

(defun sre-equal (r s)
  "Do the two SREs /r/ and /s/ describe the very same language?"
  (sre-empty-p `(or (- ,r ,s) (- ,s ,r))))

(defun sre-less-p (r s)
  "Is R a subset of S?"
  (sre-empty-p `(- ,r ,s)))

(defun sre-empty-p (r)
  "Does the SRE /r/ denote the empty language?"
  (let ((dfa (re-dfa r)))
    (notany #'(lambda (q) (dfa-state-exit-transition dfa q))
            (dfa-states dfa))))