$\Theta \rho ϵ\eta \Pi \alpha \tau \pi$

Suppose that $X$ is a set and $𝒮$ is a $\sigma$-algebra on $X$. A measure on $(X,𝒮)$ is a function $\mu :𝒮\to [0,\infty ]$ such that $\mu \left(\varnothing \right)=0$ and $$\mu \left(\bigcup _{k=1}^{\infty }{E}_k\right)=\sum _{k=1}^{\infty }\mu \left(E_k\right)$$ for every pairwise disjoint sequence $E_1,E_2,\dots \in 𝒮$.

A measure space is an ordered triple $(X,𝒮,\mu )$, where $X$ is a set, $𝒮$ is a $\sigma$-algebra on $X$, and $\mu$ is a measure on $(X,𝒮)$.