\begin{definition}[Definition:Cardinality of Finite Class/Definition 2]
Let $A$ be a class.
Let $A$ be such that:
:there exists a bijection $\phi$ from $A$ to the set $\set {1, 2, \dotsc, n} = n^+ \setminus \set 0$
where:
:$n$ is a natural number as defined by the von Neumann construction
:$n^+$ is the successor of $n$.
Then $A$ has '''cardinality $n$'''.
\end{definition}