doc/concepts.tex: Fix vertical space above subsections.

diff --git a/doc/concepts.tex b/doc/concepts.tex
index 3ab3da8..99f7884 100644 (file)
--- a/doc/concepts.tex
+++ b/doc/concepts.tex
@@ -276,6 +276,7 @@ class in a chain is called the \emph{chain head}; the most specific class is
 the \emph{chain tail}.  Chains are often named after their chain head
 classes.
 
+
 \subsection{Names}
 \label{sec:concepts.classes.names}