Michael Kay:
The second solution is Dimitre's functional programming approach. This is
the one that's closest to the way I expressed the problem above. Note that I
described a three-stage approach in which stage 2 involves computing some
function. This is a classic higher-order function. The three-step algorithm
is a function that takes two arguments: the sequence of nodes, and the
function to be computed in step 2. Dimitre's FXSL library allows you to
write the solution in this form. It takes some getting used to, but it's the
most economical way of solving the problem; and although it involves calling
the FXSL library, that's written in pure XSLT 1.0 so it should be completely
portable.
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Thank you.
I had gotten the notion that FXSL required EXSLT to work.

Thanks to all who took the time to help me.
Ragulf Pickaxe :-)