  We present a summary of: 1) the non-uniqueness problem of the Hamiltonian and
energy operators associated, in any given coordinate system, with the
generally-covariant Dirac equation; 2) two different ways to restrict the gauge
freedom so as to solve that problem; 3) the application of these two ways to
the case of a uniformly rotating reference frame in Minkowski spacetime: we
find that a spin-rotation coupling term is there only with one of these two
ways.
