proposition: Lemma clos_rst1n_sym : forall x y, clos_refl_sym_trans_1n R x y -> clos_refl_sym_trans_1n R y x.
proof: Proof. intros x y H; elim H. - constructor 1. - intros x0 y0 z D H0 H1; apply clos_rst1n_trans with y0; auto. right with x0. + destruct D; [right|left]; auto. + left. Defined.
imports: CRelationClasses Equations.Init Equations.Type.Logic Equations.Type.Relation