@Stephen_Dewitt
Thanks for the inspiration. I made a correction to the code. Maybe it is the updates but it does not work with single backslashes.
$$ \begin{array}{cccccccc}
Daily & Mo & Tu & We & Th & Fr & Sa & Su \ \hline
~Ex~ & [x] & [] & [] & [x] & [] & [] & []\
~Md~ & [] & [] & [] & [] & [] & [] & [] \
\end {array} $$