proposition: Lemma neqhead_lexiE (x y : T) s1 s2 : x != y -> (x :: s1 <= y :: s2 :> seq _) = (x < y).
proof: Proof. by rewrite lexi_cons; case: comparableP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)