proposition: Lemma wf_imm_succ r (WF: well_founded r) a b (REL: r a b) : exists c, immediate r a c.
proof: Proof. revert a REL; induction b using (well_founded_ind WF); ins. tertium_non_datur (immediate r a b) as [?|NIM]; eauto. Qed.
imports: Arith micromega.Lia Setoid Morphisms Wf_nat HahnBase HahnList HahnSets HahnRelationsBasic HahnEquational HahnRewrite HahnDom