proposition: Lemma decomp_measurable (A : set rT) (X : set T) : measurable A -> X \in decomp A -> measurable X.
proof: Proof. rewrite /decomp; case: ifP => _; first by rewrite inE => _ ->. by case: pselect => // Am _; case: cid => //= ? [_ _ _ + _]; apply. 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)