# Measure Theory/Basic Structures And Definitions

In the following section we use the convention that ${\displaystyle \,X}$ is a set and ${\displaystyle {\mathcal {P}}(X)}$ is its power set.
Usually if ${\displaystyle {\mathcal {C}}}$ is a subset of ${\displaystyle {\mathcal {P}}(X)}$ it'll be referred as class.