diff -r 90583d625648 -r 021728c71030 doc-src/Logics/preface.tex
--- a/doc-src/Logics/preface.tex	Mon May 10 15:35:03 1999 +0200
+++ b/doc-src/Logics/preface.tex	Mon May 10 16:35:22 1999 +0200
@@ -54,10 +54,14 @@
   Cube} are undocumented.  All object-logics' sources are distributed with
 Isabelle (see the directory \texttt{src}).  They are also available for
 browsing on the WWW at
-\begin{ttbox}
-http://www.cl.cam.ac.uk/Research/HVG/Isabelle/library/
-http://isabelle.in.tum.de/library/
-\end{ttbox}
+
+\begin{center}\small
+  \begin{tabular}{l}
+    \url{http://www.cl.cam.ac.uk/Research/HVG/Isabelle/library/} \\
+    \url{http://isabelle.in.tum.de/library/} \\
+  \end{tabular}
+\end{center}
+
 Note that this is not necessarily consistent with your local sources!
 
 \medskip Do not read the \emph{Isabelle's Logics} manuals before reading