\begin{table}%t6
%\centering
\par
\caption{Predicted AGN surface densities, based on (partly extrapolated) 
COMBO-17 results. Each field gives the cumulative AGN number per~deg$^2$,
brighter than~$R$ and with redshift greater than $z$, as derived from the 
two simple evolution models discussed in this paper.\label{tab:pred}}
$$
\begin{tabular}{c..@{\hspace{2em}}..@{\hspace{2em}}..@{\hspace{2em}}..}
\hline \hline
\noalign{\smallskip}
Magnitude & \multicolumn{2}{c}{$N(z>2)$\ \ } & \multicolumn{2}{c}{$N(z>3)$\ \ }
          & \multicolumn{2}{c}{$N(z>4)$ \ \ } & \multicolumn{2}{c}{$N(z>5)$ \ \ } \\
\noalign{\smallskip}
          & \multicolumn{1}{c}{PDE} & \multicolumn{1}{l}{\ PLE} & 
            \multicolumn{1}{c}{PDE} & \multicolumn{1}{l}{\ \ \ PLE} & 
            \multicolumn{1}{c}{PDE} & \multicolumn{1}{l}{\ \ PLE} & 
            \multicolumn{1}{c}{PDE} & \multicolumn{1}{l}{\ PLE} \\
\hline
$R < 20$  &  16.1 &  20.0  &   3.0 &  3.0   &   0.33 & 0.28  &  0.03 & 0.05 \\
$R < 21$  &  38.2 &  43.3  &   7.9 &  7.9   &   0.98 & 0.95  &  0.10 & 0.19 \\
$R < 22$  &  81.  &  85.   &  18.1 & 18.8   &   2.5  & 2.9   &  0.28 & 0.69 \\
$R < 23$  & 148.  & 152.   &  36.6 & 40.6   &   5.6  & 7.9   &  0.68 & 2.3  \\
$R < 24$  & 241.  & 252.   &  67.  & 81.    &  10.8  &19.7   &  1.5  & 6.7  \\
$R < 25$  & 322.  & 362.   & 101.  &147.    &  18.5  &44.8   &  2.7  &17.5  \\
\hline
\end{tabular}
$$
\end{table}