proposition: Lemma size_enum_ord n : size (enum 'I_n) = n.
proof: Proof. by rewrite -cardE card_ord. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)