Definition Diff_tagged (A B: Tpoint) := A <> B.

(* Specifications: *)
Lemma Diff_Diff_tagged : forall A B , A <> B -> Diff_tagged A B.
Lemma Diff_tagged_Diff : forall A B , Diff_tagged A B -> A <> B.
Lemma Diff_perm : forall (A B: Tpoint), A <> B -> A <> B /\ B <> A.