proposition: Lemma semiconn_ordf x y : x != y -> ordf x y || ordf y x.
proof: Proof. rewrite /ordf; case: ltngtP=>//= H. have [H1 H2]: x \in enum T /\ y \in enum T by rewrite !mem_enum. by rewrite -(nth_index x H1) -(nth_index x H2) H eq_refl. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path fintype) pcm(options)