Definition:Almost-Everywhere Equality Relation/Measurable Functions/Extended Real-Valued Functions

Definition
Let $\struct {X, \Sigma, \mu}$ be a measure space. Let $\map {\mathcal M} {X, \Sigma}$ be the set of $\Sigma$-measurable functions on $X$.

We define the $\mu$-almost-everywhere equality relation $\sim_\mu$ on $\map {\mathcal M} {X, \Sigma}$ by:


 * $f \sim_\mu g$ $\map f x = \map g x$ for $\mu$-almost all $x \in X$.

That is:


 * $\map \mu {\set {x \in X : \map f x \ne \map g x} } = 0$