proposition: Lemma big_image I (J : finType) (h : J -> I) (A : pred J) F : \big[op/x]_(i <- [seq h j | j in A]) F i = \big[op/x]_(j in A) F (h j).
proof: Proof. by rewrite big_map big_enum. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)