proposition: Lemma restr_f_assoc : associative f -> associative Build_SubCSetoid_bin_op.
proof: Proof. intros assf x y z. case z. case y. case x. intros. apply: assf. Qed.
imports: CoRN.tactics.CornTac CoRN.logic.CLogic CoRN.tactics.Step CoRN.algebra.RSetoid