--- a/Slides/Slides2.thy	Tue Jul 23 15:14:12 2013 +0200
+++ b/Slides/Slides2.thy	Tue Jul 23 15:18:15 2013 +0200
@@ -597,12 +597,12 @@
 text_raw {*
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   \mode<presentation>{
-  \begin{frame}[t]
+  \begin{frame}[b]
   \frametitle{Undecidability}%
 
-  \begin{center}
+  \begin{textblock}{7}(4,2.4)
   @{thm tcontra_def}
-  \end{center}
+  \end{textblock}
   
   \only<2>{
   \begin{itemize}