proposition: Lemma prod_salgebra_set0 : preimage_classes f1 f2 (set0 : set (T1 * T2)).
proof: Proof. exact: sigma_algebra0. 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)