Definition Inv_comp_elt_l := Inv_elt_l x +_M Inv_elt_l y.Definition Inv_comp_elt_r := Inv_elt_r y +_M Inv_elt_r x.

(* Specifications: *)
Lemma Inv_comp_invs1 : Inverses_rel Inv_comp_elt_l Inv_comp_elt_r.
Lemma Inv_comp_invs2 : Inverses_rel Inv_comp_elt_r Inv_comp_elt_l.