diff -r 9c8fc56032e3 -r 2548e7cc86fb src/Doc/Isar_Ref/document/root.tex
--- a/src/Doc/Isar_Ref/document/root.tex	Tue Dec 29 19:11:23 2015 +0100
+++ b/src/Doc/Isar_Ref/document/root.tex	Tue Dec 29 20:58:18 2015 +0100
@@ -1,6 +1,7 @@
 \documentclass[12pt,a4paper,fleqn]{report}
 \usepackage{lmodern}
 \usepackage[T1]{fontenc}
+\usepackage{amsmath}
 \usepackage{amssymb}
 \usepackage{wasysym}
 \usepackage{eurosym}