proposition: Lemma cr_union_r r r' : (r ∪ r') ^? ≡ r ∪ r' ^?.
proof: Proof. by rewrite unionC, cr_union_l, unionC. Qed.
imports: Program.Basics Arith micromega.Lia Permutation List Setoid HahnBase HahnList HahnRelationsBasic HahnSets