We consider an integrable model of a one-dimensional mesoscopic ring with the
conduction electrons coupled by a spin exchange to a magnetic impurity. A
symmetry analysis based on a Bethe Ansatz solution of the model reveals that
the current is insensitive to the presence of the impurity. We argue that this
is true for any integrable impurity-electron interaction, independent of choice
of physical parameters or couplings. We propose a simple physical picture of
how the persistent current gets protected by integrability.Comment: 5 pages, minor update