diff --git a/common.tex b/common.tex
index c3f9d3307acc34b6cddaeff87c080cc5167e668c..f1a7405beff4f727037d003b5443a57b9ba1a319 100644
--- a/common.tex
+++ b/common.tex
@@ -8,6 +8,7 @@
 \usepackage{mathtools}
 \usepackage[extreme]{savetrees}
 \usepackage{multicol}
+\usepackage{rotating}
 
 \usepackage{tikz}
 \usetikzlibrary{shapes,positioning}
@@ -40,6 +41,14 @@
 % From https://tex.stackexchange.com/a/284054
 \DeclareMathOperator*{\argmax}{argmax}
 
+% TODO annotate each definition with a reference
+\newcommand{\defref}[1]{\marginpar{
+    \begin{sideways}
+      \tiny #1
+    \end{sideways}
+  }
+}
+
 %%% Local Variables:
 %%% mode: latex
 %%% TeX-master: "master"