Math 2.0

Measure and integration Measures Concept

Countable additivity

Summary

A set function is countably additive, or σ-additive, if its value on a countable disjoint union is the sum of its values on the pieces. Countable additivity is the defining property of measures. It is stronger than finite additivity, and it is what makes limit theorems such as monotone convergence work.

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Further reading

  1. Web https://en.wikipedia.org/wiki/Sigma-additive_set_function
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Changed2 November 2026

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