A set $T$ is transitive if every element of $T$ is a subset of $T$.
The following statements are equivalent:
$T$ is transitive.
- \[\bigcup T\subseteq T.\]
- \[T\subseteq\powerset(T).\]
A set $T$ is transitive if every element of $T$ is a subset of $T$.
The following statements are equivalent:
$T$ is transitive.
- \[\bigcup T\subseteq T.\]
- \[T\subseteq\powerset(T).\]