> Can't you run a three-level for-each so that you can compute all
> three numbers in one go?

I have to admit, I don't understand what you have in mind here. But
that may be just because I'm dizzy with the prospect of one of the
earlier suggestions working. In any case, I won't ask you to explain
it in further detail unless I can't get one of the other suggestions
working reasonably soon.

Thanks, both for this and all you do on xsl-list.