[OS X TeX] Missing $ inserted in a "variations" environment (SOLVED)

[ewan.Delanoy at math.unicaen.fr]

>It looks like what you should really do is split off the border you're
>creating with \bg into a separate column of the table, as the
>{variations} environment doesn't know how to combine this nicely with
>math-mode content.


    Thanks a lot for your very exhaustive answer Jonathan. It works now,
exactly as you predicted. The "i XXXX"
trick will certainly be useful for me in other situations.

                                   Ewan