--- a/Slides/graph.sty	Mon Feb 15 21:48:57 2016 +0100
+++ b/Slides/graph.sty	Wed Feb 24 21:08:35 2016 +0000
@@ -5,7 +5,8 @@
 \usetikzlibrary{fit}
 \usepackage{graphicx} 
 \usepackage{pgfplots}
-
+\usetikzlibrary{arrows}
+\usetikzlibrary{shapes}
 
 \newenvironment{bubble}[1][]{%
 \addtolength{\leftmargini}{4mm}%