\begin{tabular}{|l|l|l|l|c|c|}
\hline \multicolumn{2}{|c|}{Proof obligations } & \provername{Alt-Ergo 0.99.1} & \provername{Coq 8.7.1} \\ 
\hline
\explanation{G1} & & \valid{0.00} & \noresult\\ 
\hline
\explanation{G2} & & \unknown{0.00} & \noresult\\ 
\cline{2-3}
 & \explanation{G2.0} & \unknown{0.00} & \unknown{0.29} \\ 
\cline{2-4}
 & \explanation{G2.1} & \valid{0.00} & \noresult\\ 
\hline
\explanation{G3} & & \valid{0.00} & \noresult\\ 
\hline \end{tabular}