Definition:Inductive Class

Definition
Let $A$ be a class.

Then $A$ is inductive iff:


 * $(1): \quad \varnothing \in A$
 * $(2): \quad \forall x: \left({x \in A \implies x^+ \in A}\right)$

where $x^+$ is the successor of $x$.

That is, where:
 * $x^+ = x \cup \left\{{x}\right\}$