Definition:Subclass

Definition
Let $A$ and $B$ be classes.

Then $A$ is a subclass of $B$, and we write $A \subseteq B$, :


 * $\forall x: \paren {x \in A \implies x \in B}$

where $x \in A$ denotes that $x$ is an element of $A$.

Also see

 * Definition:Subset