  By examining the behaviour of the "SLAC" lattice derivative operators, it is
found that lattices with an even number of sites have a somewhat strange
self-consistency requirement for extra structure in the spatial derivative
operator, which is not needed by lattices having an odd number of sites, and
which is not at all obvious from a first-principles derivation. The general
implications of this extra required structure are not, as yet, completely
clear.
