  This memoir is dedicated to the late Francis Hayin Ree, a formative influence
shaping my work in statistical mechanics. Between 1963 and 1968 we collaborated
on nine papers published in the Journal of Chemical Physics. Those dealt with
the virial series, cell models, and computer simulation. All of them were
directed toward understanding the statistical thermodynamics of simple model
systems. Our last joint work is also the most cited, with over 1000 citations,
"Melting Transition and Communal Entropy for Hard Spheres", submitted 3 May
1968 and published that October. Here I summarize my own most recent work on
compressible time-reversible two-dimensional maps. These simplest of model
systems are amenable to computer simulation and are providing stimulating and
surprising results.
