Fixpoint eqm_bool (x y : Map bool) {struct y} : bool :=
  match x, y with
  | M0, M0 => true
  | M0, M1 _ _ => false
  | M0, M2 _ _ => false
  | M1 _ _, M0 => false
  | M1 a b, M1 c d => Neqb a c && eq_bool b d
  | M1 _ _, M2 _ _ => false
  | M2 _ _, M0 => false
  | M2 _ _, M1 _ _ => false
  | M2 a b, M2 c d => eqm_bool a c && eqm_bool b d
  end.

Lemma orb_incr : forall b0 b1 b2 b3 : bool, leb b0 b1 -> leb b2 b3 -> leb (b0 || b2) (b1 || b3).