Definition:Proper Relational Structure

Definition
Let $A$ be a set or class.

Let $\RR$ be a relation on $A$.

Then $\struct {A, \RR}$ is a proper relational structure :


 * For each $a \in A$, the preimage $\map {\RR^{-1} } a$ of $a$ under $\RR$ is a set (or small class).