\documentclass[fleqn,leqno]{article}
\usepackage{hypertlabook}
\pdftitle{Hint}
\begin{popup}
\subsection*{Hint}

First prove the soundness of the rule
 \[ \tlrule{[]F => <>G}{[]F => []<>G}
 \]
\mbox{}
\end{popup}
\makepopup