You can take and to be two disjoint sets with countable complements and for i > 2. Then the left-hand side of the definition of countably additive measure is 1 while the right-hand side is 2.
You can take and to be two disjoint sets with countable complements and for i > 2. Then the left-hand side of the definition of countably additive measure is 1 while the right-hand side is 2.