  A new method is developed for treating the effect of the neutron-proton mass
difference in isospin-violating nuclear forces. Previous treatments utilized an
awkward subtraction scheme to generate these forces. A field redefinition is
used to remove that mass difference from the Lagrangian (and hence from
asymptotic nucleon states) and replace its effect by effective interactions.
Previous calculations of static Class II charge-independence-breaking and Class
III charge-symmetry-breaking potentials are verified using the new scheme,
which is also used to calculate Class IV nuclear forces. Two-body forces of the
latter type are found to be identical to previously obtained results. A novel
three-body force is also found. Problems involving Galilean invariance with
Class IV one-pion-exchange forces are identified and resolved.
