Interval Coalesce Problem in XSLT

I encountered this problem in the (highly recommended) SQL Design Patterns by
Vadim Tropashko, and have been waiting for a chance to implement something
similar in an XSLT. I finally had the chance: XML documents describing
observations over time intervals, which I have to (maximally) coalesce. In
other words, if an object was observed from different viewpoints in the same
location during certain time intervals, I can coalesce all those time
intervals to say that the object was at that location during a time interval
covering all those smaller intervals.

I don't like "Please read my blog post" mail, but I thought this might
actually interest people. I'm satisfied that my solution is correct, but I'd
be interested in finding out if it's not! So if it does interest you, see
http://slideguitarist.blogspot.com/2011/03/interval-coalesce-with-xslt.html.
I'd like to see any performance suggestions.

Tony Nassar Ph.D.
Palantir Technologies | Forward Deployed Engineer
tnassar@xxxxxxxxxxxxxxxx | 650-387-6502 | Pager 888-913-2793