Proof using A order order_trans.
intros antisym l1; elim l1; clear l1; simpl in |- *; auto.
intros l2 H1 H2 H3; apply sym_equal; apply permutation_nil_inv.
apply permutation_sym; auto.
intros a l1 Rec l2; case l2; simpl in |- *.
intros H; absurd (length (a :: l1) = length (A:=A) nil).
simpl in |- *; red in |- *; intros; discriminate.
apply permutation_length; auto.
intros a0 l H H0 H1.
cut (a = a0).
intros H3; apply f_equal2 with (f := cons (A:=A)); auto.
apply Rec; auto.
apply permutation_inv with (a := a); auto.
pattern a at 2 in |- *; rewrite H3; auto.
apply ordered_inv with (1 := H0); auto.
apply ordered_inv with (1 := H1); auto.
generalize (permutation_in _ a _ _ H); simpl in |- *;
(intros H2; case H2; auto; clear H2; intros H2).
generalize (permutation_in _ a0 _ _ (permutation_sym _ _ _ H)); simpl in |- *;
(intros H3; case H3; auto; clear H3; intros H3).
apply antisym.
apply ordered_trans with (1 := H0); auto.
apply ordered_trans with (1 := H1); auto.
Qed.
End ordered.
Hint Constructors ordered : core.
Arguments ordered [A].

(* Ordered list are preserved by maps *)
Theorem ordered_map_inv :
forall (A B : Type) (order : A -> A -> Prop) (g : B -> A) (l : list B),
ordered (fun x y => order (g x) (g y)) l -> ordered order (map g l).