A <class in set theory> is a collection
$$
M=\{x\in V:V\models\psi(x,a_1,\ldots,a_r)\}
$$
defined by a formula $\psi$, with set parameters if these are allowed by the chosen convention. It is a set-class if there is an $m\in V$ whose elements are exactly the members of $M$. Otherwise it is a <proper class>.

Solution

Past exam of the mathematics course of the University of Cambridge / 2025 / ii / Paper 4 / 16H / a / Solution

 Solution (source code)