proposition: Lemma set_subset_max_elt (S: r' ⊆ r) : max_elt r ⊆₁ max_elt r'.
proof: Proof. unfold max_elt, inclusion, set_subset in *; intuition; eauto. Qed.
imports: HahnBase HahnList HahnSets HahnRelationsBasic HahnEquational HahnRewrite Arith Setoid