Definition 5.10 (Cardinality)

#Definition

A set is called $finite$ , if it contains only finitely many elements, i.e. there is a number $n \in N$ , where the set contains exactly $n$ elements

The $cardinality$ of a set $M$ is

| M | : = {\begin{cases} The number of elements in M, if M is finite \\ \infty, otherwise \end{cases}