more robust document setup;

--- a/src/ZF/document/root.tex	Wed Aug 29 20:16:22 2012 +0200
+++ b/src/ZF/document/root.tex	Wed Aug 29 20:46:47 2012 +0200
@@ -1,6 +1,7 @@
 \documentclass[11pt,a4paper]{article}
 \usepackage{graphicx,isabelle,isabellesym}
 \usepackage{amssymb}
+\usepackage[english]{babel}
 
 % this should be the last package used
 \usepackage{pdfsetup}