  We describe an exact derivation of the total nondissipative transverse force
acting on a quantized vortex moving in a uniform background. The derivation is
valid for neutral boson or fermion superfluids, provided the order parameter is
a complex scalar quantity. The force is determined by the one-particle density
matrix far away from the vortex core, and is found to be the Magnus force
proportional to the superfluid density.
