# Definition:Class/Zermelo-Fraenkel/Class Variables

In deriving general results about $\textrm{ZF}$ which mention classes, it is often convenient to have class variables, which denote an arbitrary class.
By convention, these variables are taken on $\mathsf{Pr} \infty \mathsf{fWiki}$ to be the (start of) the capital Latin alphabet, i.e. $A, B, C$, and so on.