End of NBO

Signed-off-by: Riccardo Finotello <riccardo.finotello@gmail.com>

sec/part1/introduction.tex

@@ -1280,7 +1280,7 @@ The field $\cA^a$ forms a vector representation of the group \SO{D-1-p} and from
   \label{fig:dbranes:chanpaton}
 \end{figure}
 
-It is also possible to add non dynamical degrees of freedom to the open string endpoints.
+It is also possible to add non dynamical degrees of freedom (\dof) to the open string endpoints.
 They are known as \emph{Chan-Paton factors}~\cite{Paton:1969:GeneralizedVenezianoModel}.
 They have no dynamics and do not spoil Poincaré or conformal invariance in the action of the string.
 Each state can then be labelled by $i$ and $j$ running from $1$ to $N$.