Set of Finite Strings/Examples/Over One Element

Example of Set of Finite Strings
Let $\Sigma$ be the alphabet defined as:
 * $\Sigma = \set a$

Then the set of finite strings $\Sigma^*$ over $\Sigma$ is:
 * $\Sigma^* = \set {\epsilon, a, aa, aaa, aaaa, \ldots}$

where $\epsilon$ denotes the null string.