Hey,
thanks for your answer.
> (user input) --> (openmath) --> (text string) --> (Maxima)
>
correct
> I think there is some code in maxima/share to convert OpenMath XML
> to Maxima expressions. (Or maybe it goes in the other direction ...
> I don't remember for sure.)
>
Hm.. maybe you can give me another hint for it?!
Until now, I only found functionality to get MathML out (not in).
> In any event, if you have XML at hand, skip the text conversion
> and go directly to Maxima.
>
It would be so nice if this is already possible.