proposition: Lemma index_enum_ord (i : 'I_n) : index i (enum 'I_n) = i.
proof: Proof. by rewrite -[in LHS](nth_ord_enum i i) index_uniq ?(enum_uniq, size_enum_ord). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(path div)