proposition: Lemma semiconn_ords : forall x y, x != y -> ords x y || ords y x.
proof: Proof. elim=>[|x xs IH][|y ys]//=. case:ifP => H1 H2; rewrite eq_sym H1. - by apply: IH; move: H2; rewrite -eqseqE /= H1 andTb. by rewrite semiconnex // H1. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path fintype) pcm(options)