  We say that the vanishing viscosity limit holds in the classical sense if the
velocity for a solution to the Navier-Stokes equations converges in the energy
norm uniformly in time to the velocity for a solution to the Euler equations.
We prove, for a bounded domain in dimension 2 or higher, that the vanishing
viscosity limit holds in the classical sense if and only if a vortex sheet
forms on the boundary.
