Redefining "in" "operator"

["Alejandro R. Mosteo" <alejandro@mosteo.com>]

It just dawned on me that I could want to define an "in" function for a 
couple of my types, but this is not allowed.

I tried searching but the term is so general that I only find unrelated 
threads, so here it goes:

Are there special reasons not to allow something like that? I think "in" 
is not an operator in the Ada RM sense but now I'm curious why the 
special treatment.

It's merely to avoid subversion of the default behavior? Couldn't it 
only be allowed for couples of types where it doesn't apply?

Thanks,
Álex.