A class of sets $\mathfrak{C}\subseteq\mathscr{M}$ is called definable when for any representable class $\mathfrak{S}$, the class $\mathfrak{C}\cap\mathfrak{S}$ is representable.
A class of sets $\mathfrak{C}\subseteq\mathscr{M}$ is called definable when for any representable class $\mathfrak{S}$, the class $\mathfrak{C}\cap\mathfrak{S}$ is representable.