Added paragraph about training of the auto-encoder

Signed-off-by: Jim Martens <github@2martens.de>

body_expose.tex

@@ -327,7 +327,9 @@ updates of each of the aforementioned components:
     \item Minimize \(\mathcal{L}_{error}\) and \(\mathcal{L}_{adv-d_z}\) by updating weights of \(e\) and \(g\).
 \end{itemize}
 
-
+Practically, the auto-encoder is trained separately for every
+object class that is considered "known". Pidhorskyi et al trained
+it on the MNIST\cite{Lecun1998} data set, once for every digit.
 
 \section{Contribution}