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