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*}