John, All:
Your post of 20 Apr 2010 had an exciting quiz; but somehow no one has
volunteered answers!
I would love to hear the answers... (I suspect that my guesses are wrong!)
Suppose we have an overall system consisting of two
subsystems, A and B. The overall system is closed
and isolated, so its energy is constant. However,
subsystem A can exchange energy with subsystem B.
Suppose subsystem B is large enough and well behaved
enough to serve as a heat bath. OTOH subsystem A
is much smaller, consisting of just two spin-1/2
particles (four microstates, three energy levels).