Power set

[summary: The power set $\mathcal P (X)$ of a set $X$ is the set of all subsets of $X$. That is, if $Y \subseteq X$, then $Y \in \mathcal P (X)$. ]

The power set $\mathcal P (X)$ of a set $X$ is the set of all subsets of $X$. That is, if $Y \subseteq X$, then $Y \in \mathcal P (X)$.