proposition: Lemma sigma_algebra_bigcup (A : (set T)^nat) : (forall i, <<s D, G >> (A i)) -> <<s D, G >> (\bigcup_i (A i)).
proof: Proof. by case: smallest_sigma_algebra A. 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)