# Category:Subsets

A set $S$ is a subset of a set $T$ if and only if all of the elements of $S$ are also elements of $T$, and it is written $S \subseteq T$.
If the elements of $S$ are not all also elements of $T$, then $S$ is not a subset of $T$:
$S \nsubseteq T$ means $\neg \paren {S \subseteq T}$