In the following table, why does the double line before the diff column not go through? I guess all the multicolumn{1} are wrong? How can I fix it?
\begin{table}
\centering
\begin{tabular}{|l||c|c|c|c|c|c||r|}\hline
\multicolumn{1}{|c||}{} &
\multicolumn{3}{c|}{Model 1} &
\multicolumn{3}{c|}{Model 2} &
\multicolumn{1}{||r|}{}\\
\multicolumn{1}{|c||}{Task} &
\multicolumn{1}{c}{(a)} &
\multicolumn{1}{c}{(b)} &
\multicolumn{1}{c|}{(c)} &
\multicolumn{1}{c}{(a)} &
\multicolumn{1}{c}{(b)} &
\multicolumn{1}{c}{(c)} &
\multicolumn{1}{||r|}{diff}\\\hline
Foo & 1 & 2 & 3 & A & B & C & + \\
Bar & 1 & 2 & 3 & A & B & C & + \\\hline
\end{tabular}
\caption{whatever}\label{tab:whatever}
\end{table}


\begin{tabular}{@{}lccccccc@{}}– Jan 11 '11 at 10:45