Cardinality/Examples/Powerset of Empty Set

Example of Cardinality
Let:
 * $S_5 = \powerset \O$

where:
 * $\O$ denotes the empty set
 * $\powerset \O$ denotes the power set of $\O$.

The cardinality of $S_5$ is given by:
 * $\card {S_5} = 1$

Proof
By Power Set of Empty Set, we have that:
 * $\powerset \O = \set {\O}$

Thus $\powerset \O$ contains exactly $1$ element, that is: $\O$.

Hence the result by definition of cardinality.