proposition: Lemma enum_valP A i : @enum_val A i \in A.
proof: Proof. suff: enum_val i \in enum A by rewrite mem_enum. by apply: mem_nth; rewrite -cardE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)