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This category contains results about Subclasses.
Definitions specific to this category can be found in Definitions/Subclasses.

Let $A$ and $B$ be classes.

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

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

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