*** Welcome to piglix ***

Countably additive


In mathematics, additivity and sigma additivity (also called countable additivity) of a function defined on subsets of a given set are abstractions of the intuitive properties of size (length, area, volume) of a set.

Let be a function defined on an algebra of sets with values in [−∞, +∞] (see the extended real number line). The function is called additive, or finitely additive, if, whenever A and B are disjoint sets in , one has


...
Wikipedia

...