\documentclass[fleqn,leqno]{article}
\usepackage{hypertlabook}
\pdftitle{The Body of Algorithm Euclid}
\begin{popup}
\subsection*{The Body of Algorithm \emph{Euclid}}

\begin{nopcal}
while (x # y) { if (x < y) { y := y - x }
                else       { x := x - y }
              } 
\end{nopcal}
\begin{tlatex}
 \@x{ {\p@while} {\p@lparen} x \.{\neq} y {\p@rparen} {\p@lbrace} {\p@if}
 {\p@lparen} x \.{<} y {\p@rparen} {\p@lbrace} y \.{:=} y\@s{0.10} \.{-} x
 {\p@rbrace}}%
 \@x{\@s{85.13} {\p@else}\@s{24.59}\@s{9.09}  {\p@lbrace} x\.{:=} x \.{-} y
 {\p@rbrace}}%
\@x{\@s{75.54} {\p@rbrace}}%
\end{tlatex}

\end{popup}
\makepopup