proper latex setup;

--- a/src/Doc/Tutorial/document/root.tex	Sat Mar 05 21:23:28 2016 +0100
+++ b/src/Doc/Tutorial/document/root.tex	Sat Mar 05 22:04:33 2016 +0100
@@ -1,6 +1,6 @@
 \documentclass{article}
 \usepackage{cl2emono-modified,isabelle,isabellesym}
-\usepackage{proof,amsmath,amsfonts}
+\usepackage{proof,amsmath,amsfonts,amssymb}
 \usepackage{latexsym,wasysym,verbatim,graphicx,tutorial,ttbox,comment}
 \usepackage{eurosym}
 \usepackage[english]{babel}