proposition: Lemma partial_fun2_axioms y: lf_axiom (fun x=>Vf f (J x y))(im_of_singleton (inverse_graph (source f)) y) (target f).
proof: Proof. move=> t /iim_graph_P [u /set1_P ->]; fprops. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)