- now intros w; rewrite Rmax_left;[ | apply Rge_le, Ropp_le_ge_contravar].
- now intros w; rewrite Rmax_right; [ | apply Rge_le, Ropp_le_ge_contravar].
Qed.

Lemma Rmin_assoc : forall x y z, Rmin x (Rmin y z) =
Rmin (Rmin x y) z.