Enumerate Multicolumns

\usepackage{multicols}

...

% List all items in the enumerate, using the specified number of columns (3 in the below example)
\begin{multicols}{3}
  \begin{enumerate}
    \item $g_1 H = g_2 H$;
    \item $Hg_2^{-1} = Hg_1^{-1}$;
    \item $g_1H \subseteq g_2H$;
    \item $g_2\in g_1H$;
    \item $g_1^{-1}g_2\in H$.
  \end{enumerate}
\end{multicols}