We limit ourselves to summarize in the following table some of the most general special cases that have been proved more recently.

\begin{center}
\begin{tabular}{cc}
	Conditions & Reference \\
	\hline 
	$m=0$ and $k=0$ &  \cite{Leven-2016} \\
	$\<\cdot , e_{n-d}h_d\>$ & Section~\ref{ssec:oor_square}\\
	$q=0$ & Section~\ref{ssec:oor_square}
	\end{tabular}
\end{center}

We would like to mention here the early proof by Can and Loehr \cite{Can-Loehr-2006} of the special case $m=k=0$ and $\<\cdot , e_{n}\>$.