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