fact: Definition adjacent A (rel: relation A) a b := ⟪ LA_ac : forall c, rel b c -> rel a c ⟫ /\ ⟪ LA_ca : forall c, rel c b -> rel^? c a ⟫ /\ ⟪ LA_cb : forall c, rel c a -> rel c b ⟫ /\ ⟪ LA_bc : forall c, rel a c -> rel^? b c ⟫.
imports: HahnBase HahnRelationsBasic HahnRewrite Setoid