Basic Universe is Inductive

Theorem
Let $V$ be a basic universe.

Then $V$ is an inductive class.

Proof
By definition of basic universe, $V$ is a class containing all sets as elements.

By the :
 * the empty class $\O$ is a set.

Hence $\O$ is an element of $V$.

By the, if $x$ is a set, then $\powerset x$ is a set.

By definition of power set:
 * $\set x \subseteq \powerset x$

By the, $\set x$ is a set.

By the, if $x$ is a set, then $\bigcup x$ is a set.

Thus $x \cup \set x$ is a set.

The result follows.