--- a/Slides/document/root.tex	Wed Apr 13 13:41:52 2011 +0100
+++ b/Slides/document/root.tex	Wed Apr 13 13:44:25 2011 +0100
@@ -19,6 +19,7 @@
 \usetikzlibrary{automata}
 \usetikzlibrary{shapes}
 \usetikzlibrary{shadows}
+\usetikzlibrary{positioning}
 %%%\usetikzlibrary{mindmap}
 
 \usepackage{graphicx}