 Then formula_19 and formula_20 are equivalent, since all sets outside of formula_21 have formula_22 and formula_2 measure zero, and a set inside formula_24 is a formula_1-null set or a formula_2-null set exactly when it is a null set with respect to Lebesgue measure.Look at some measurable space formula_3 and let formula_1 be the counting measure, so

where formula_30 is the cardinality of the set a.So the counting measure has only one null set, which is the empty set.