latex の Beamer についての質問です. ( Mac です ) 1 文章 ( a ) 文章 ( b ) 文章 2 文章 を枠で囲むようなものを作りたいのですが、試しに次のように入力してもうまくいきません.やり方を教えて頂けると嬉しいです。 ¥begin{frame}{Baseline Model : No Congestion} ¥begin{itembox}[l]{Proposition 1} Suppose that for every environment $G$ and for every pair of agent $i$ and agent $j$ who share a club in $G$ , $w( i , j , G ) = 1$ . then ¥begin{enumerate}[1.] ¥item If $n_{a} - 1 > c > 0$ : ¥begin{enumerate}[(a)] ¥item $G$ is a Minimally Connected environment of class $K(G)¥geq c$ if and only if G is OCS . ¥item The Grand Club is the unique PE and SE environment . ¥end{enumerate} ¥item If $c > n_{a} - 1 , the Empty environment is the unique OCS , PE and SE and environment. ¥end{enumerate} ¥end{itembox} ¥end{frame} ¥end{document}