Differencing a major mode from its derived modes

[chem]

Hi, 
I would like to add allout mode only to text-mode.  That is, I don't
want allout mode to propagate to all the derived modes, like message
mode, etc.

I tried, using a:
 - if test on the major-mode, and it's not working
 - (if  (get major-mode 'derived-mode-parent)..., not working neither.

It seems that the major-mode on which the derived mode is based is
actually loaded.  Thus, all the hooks are made.  Only then, the
customization of the derived mode are done.  Then, I really don't know
how to isolated the parent from its children.  If someone has a
solution, it would be nice.

Thanks                            
                                       
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Chemtov