[relax-ng] Closure

I have stuck my neck out and claimed that RNG is closed under
intersection.  Is it?  Also Tim Bray wants to know if RNG
is closed under set difference.  My guess is 'no', but I'd like
to know for sure, or know that it isn't known.

-- 
John Cowan <>     http://www.reutershealth.com
I amar prestar aen, han mathon ne nen,    http://www.ccil.org/~cowan
han mathon ne chae, a han noston ne 'wilith.  --Galadriel, _LOTR:FOTR_