Symbols:Set Theory/Deprecated Symbols/Subset

Subset
$\subset$ is sometimes used to mean:
 * $S$ is a subset of $T$

in the sense that $S$ is permitted to equal $T$.

That is, for which we have specified as $S \subseteq T$.

Although many sources use this interpretation, it is emphatically not recommended, as it can be the cause of considerable confusion.