Canonical Structure Prod_Hom : Setoid := Equal_Pmor_equiv.(* composition *)

Definition Comp_Pmor (a b c : POb) (f : Prod_Hom a b) 
  (g : Prod_Hom b c) := Build_Pmor (Hom_l f o Hom_l g) (Hom_r f o Hom_r g).

Lemma Comp_Pmor_congl : Congl_law Comp_Pmor.