Section d_cat.
Variable C : Category.
Definition DHom (a b : C) := b --> a.
(* construire un Comp_Type *)
Definition Comp_Darrow (a b c : C) (df : DHom a b) (dg : DHom b c) := dg o df.
Definition Comp_Dual := Build_Comp Comp_dual_congl Comp_dual_congr.

Lemma Assoc_Dual : Assoc_law Comp_Dual.