proposition: Lemma iso_trans_ex_rw : forall x y, are_isomorphic x y = (exists f, Transformation.bijective x y f).
proof: Proof. ir; ap iff_eq; ir. sh (isotrans x y). wr iso_isotrans_rw; am. nin H. uhg. sh (Function.create x x0). wr trans_map_bijective; am. Qed.
imports: set_theory