proposition: Lemma rt_rt r : r ＊ ⨾ r ＊ ≡ r ＊.
proof: Proof. unfold seq; split; red; ins; desf; eauto using rt_trans, rt_refl. Qed.
imports: Program.Basics Arith micromega.Lia Permutation List Setoid HahnBase HahnList HahnRelationsBasic HahnSets