proposition: Lemma relU_sym' (T : Type) (e e' : rel T) : symmetric e -> symmetric e' -> symmetric (relU e e').
proof: Proof. move => sym_e sym_e' x y /=. by rewrite sym_e sym_e'. Qed.
imports: Coq(Setoid Morphisms) mathcomp(all_ssreflect) GraphTheory(edone)