proposition: Lemma finI_from_countable (I : pointedType) T (D : set I) (f : I -> set T) : countable D -> countable (finI_from D f).
proof: Proof. move=> ?; apply: (card_le_trans (card_image_le _ _)). exact: fset_subset_countable. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed