Let $M = (\mathbb{R}, \mathcal{B}(\mathbb{R}))$ be the
D5072: Standard real borel measurable space.
A
D3161: Random real number $X \in \text{Random}(\mathbb{R})$ is
symmetric about $a \in \mathbb{R}$ if and only if
\begin{equation}
\forall \, B \in \mathcal{B}(\mathbb{R}) :
\mathbb{P}(X \in B) = \mathbb{P}(2 a - X \in B)
\end{equation}
