proposition: Lemma prod_salgebra_bigcup (F : _^nat) : (forall i, preimage_classes f1 f2 (F i)) -> preimage_classes f1 f2 (\bigcup_i (F i)).
proof: Proof. exact: sigma_algebra_bigcup. Qed.
imports: mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra boolp classical_sets functions) mathcomp(cardinality fsbigop ) reals ereal signed topology normedtype sequences esum numfun HB(structures)