Proof. Recall that
\begin{equation*} S_3 = \{e,(12),(13),(23),(123),(132)\}. \end{equation*}
\begin{align*} (12) &= (12) \\ (12)(12) &= e \\ \end{align*}
\begin{align*} (13) &= (13) \\ (13)(13) &= e \\ \end{align*}
\begin{align*} (23) &= (23) \\ (23)(23) &= e \\ \end{align*}
\begin{align*} (123) &= (123) \\ (123)(123) &= (132) \\ (123)(123)(123) &= e \\ \end{align*}
\begin{align*} (132) &= (132) \\ (132)(132) &= (123) \\ (132)(132)(132) &= e \\ \end{align*}