--- a/style.sty	Fri May 01 21:30:13 2015 +0100
+++ b/style.sty	Thu Sep 24 15:58:48 2015 +0100
@@ -9,6 +9,8 @@
 \definecolor{darkblue}{rgb}{0,0,0.6}
 \usepackage[colorlinks=true,urlcolor=darkblue,linkcolor=darkblue]{hyperref}
 
+%%% for trees
+%% http://anorien.csc.warwick.ac.uk/mirrors/CTAN/graphics/pgf/contrib/forest/forest.pdf
 
 \newcommand\grid[1]{%
 \begin{tikzpicture}[baseline=(char.base)]