proposition: Lemma ct_begin r : r⁺ ≡ r ⨾ r ＊.
proof: Proof. unfold seq; split; red; ins; desf; rewrite t_step_rt in *; eauto. Qed.
imports: Program.Basics Arith micromega.Lia Permutation List Setoid HahnBase HahnList HahnRelationsBasic HahnSets