# Equivalence (measure theory)

In mathematics, and specifically in measure theory, equivalence is a notion of two measures being "the same".

## Definition

Let (X, Σ) be a measurable space, and let μ, ν : Σ → R be two signed measures. Then μ is said to be equivalent to ν if and only if each is absolutely continuous with respect to the other. In symbols:

$\mu \sim \nu \iff \mu \ll \nu \ll \mu.$

Equivalence of measures is an equivalence relation on the set of all measures Σ → R.