proposition: Lemma rev_ord_proof n (i : 'I_n) : n - i.+1 < n.
proof: Proof. by case: n i => [|n] [i lt_i_n] //; rewrite ltnS subSS leq_subr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(path div)