  We construct integrators to be used in Hamiltonian (or Hybrid) Monte Carlo
sampling. The new integrators are easily implementable and, for a given
computational budget, may deliver five times as many accepted proposals as
standard leapfrog/Verlet without impairing in any way the quality of the
samples. They are based on a suitable modification of the processing technique
first introduced by J.C. Butcher. The idea of modified processing may also be
useful for other purposes, like the construction of high-order splitting
integrators with positive coefficients.
