Region questions

[Hugh Hoover <heh>]

I've started on regions, assuming that they will be subclasses of Heaper,
and will have approximately the protocol you wrote out in your note yesterday.
  I have a couple of questions on how everybody thinks these beasties should
act.   But First! a message from our ...  no well, a note on hierarchy.
I've set things up so that Region and DiscreteRegion are both abstract
superclasses.  The two implementation regions I'm creating are
LinearRegion (should that be LinearDiscreteRegion?) and SetRegion.  I'll do
CompositeRegion later.  LinearRegion is simple, and specified with a lower
and upper bound (IntegerVars, so far).  It provides an extra bit of protocol
for the bounds (lowerBound, upperBound).
  Now, the questions:
1) If the region is empty, which messages should blast?  I currently don't
blast on any, the only distinction is that isEmpty is true.  Of course,
lowerBound and upperBound are meaningless, so they probably should blast.
2) who (class-wise) is resposible for setting up the regionType?  Where do
we get the appropriate set of orders and dsps?
2a) who (programmer-wise) is responsible for setting up the regionType? Where
do we get the appropriate set of orders and dsps?

--Hugh
p.s.
  lowerBound (inclusive) to upperBound (exclusive)