\documentclass[fleqn,leqno]{article}
\usepackage{hypertlabook}
\pdftitle{ASCII Text}
\fixverbatim
\begin{popup}
\begin{verbatim*}
seq ** iseq == [i \in (Nat \ {0}) |-> 
                  IF i =< Len(seq) THEN seq[i]
                                   ELSE iseq[i - Len(seq)]]

Inv == /\ TypeOK
       /\ (Len(ch) =< N) 
       /\ Input = (out \o ch) ** in
\end{verbatim*}
\end{popup}
\makeasciipopup