proposition: Lemma enum_val_nth A x i : @enum_val A i = nth x (enum A) i.
proof: Proof. by apply: set_nth_default; rewrite cardE in i *. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)