Let $P = (\Omega, \mathcal{F}, \mathbb{P})$ be a D1159: Probability space such that

(i)	$X : \Omega \to [-\infty, \infty]$ is a D4381: Random basic number on $P$
(ii)	\begin{equation} \mathbb{E} |X| < \infty \end{equation}

The expectation of $X$ on $P$ is the D1699: Basic number \begin{equation} \mathbb{E}_{\mathbb{P}} X : = \mathbb{E}_{\mathbb{P}} X^+ - \mathbb{E}_{\mathbb{P}} X^- \end{equation}