proposition: Lemma cr_rt 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