Add Parametric Relation {A} : (Ensemble A) Same_set
    reflexivity proved by (Same_set_refl A)
    symmetry proved by (Same_set_sym A)
    transitivity proved by (Same_set_trans A) as Same_set_rel.

Lemma Intersection_Union_distr_l: forall A P Q R, Same_set (Intersection A (Union A Q R) P) (Union A (Intersection A Q P) (Intersection A R P)).