Kleene Star
Kleene star or Kleene Closure.
Given a set $V$.
\[\begin{eqnarray} V^{0} & := & \{ \epsilon \} \nonumber \\ V^{1} & := & V \nonumber \\ V^{i+1} & := & \{wv \mid w \in V^{i}, v \in V\} \end{eqnarray}\]Kleene star of $V$ is
\[V^{*} := \bigcup_{i \ge 0} V^{i} .\]