Axiom:Axiom of Infinity

Axiom
There exists a set containing a set with no elements and the successor of each of its elements.


 * $\exists x: \left({\left({\exists y: y \in x \land \forall z: \neg \left({z \in y}\right)}\right) \land \forall u: u \in x \implies \left({u \cup \left\{{u}\right\} \in x}\right)}\right)$

In this context, the successor of the set $u$ is defined as $u \cup \left\{{u}\right\}$.

Note that the symbols $\cup$ and $\left\{\right\}$ are used here, whereas a strict presentation of this axiom would not use them, as they have not strictly speaking been defined.