proposition: Lemma null_set_setU A B : measurable A -> measurable B -> mu A = 0 -> mu B = 0 -> mu (A `|` B) = 0.
proof: Proof. move=> mA mB A0 B0; rewrite measureUfinl/= ?A0//= ?B0 ?add0e. by apply/eqP; rewrite oppe_eq0 -measure_le0/= -A0 measureIl. 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)