we will need to specify the functional form of the constraint energy and the constraint is no longer a purely geometrical object. At first glance, this would appear to complicate further the already complex algebra of constrained motions [@fixman74]. However, we will propose an algorithm for making moves which is simple to implement and which automatically ensures that the correct equilibrium averages are computed.

The second half of the paper considers a mundane—but nevertheless important—problem, namely how to evaluate the energy of a molecule made up of rigid subcomponents. We propose a consistent framework for avoiding the computation of constant terms and for imposing energy cutoffs. We extend this to the computation of the generalized Born solvation term and we describe a simple method for computing the solvent accessible surface area which has a bounded error.

Generalized Monte Carlo moves
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We begin by assembling some techniques for combining Monte Carlo moves. We define an “$E$ move” as an ergodic move which preserves $\exp(-\beta E)$ as the invariant distribution, where $\beta = 1/(kT)$ and $k$ is the Boltzmann constant. (Here, “ergodic” implies that the move allows all relevant portions to configuration space to be explored.) Note that a zero move 