proposition: Lemma prod_salgebra_setC A : preimage_classes f1 f2 A -> preimage_classes f1 f2 (~` A).
proof: Proof. exact: sigma_algebraC. 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)