  It has been argued recently that an inhomogeneous system could rotate
spontaneously in its ground state - hence a 'time crystal' which is periodic in
time. In this note we present a very simple example: a superfluid ring threaded
by a magnetic field which develops a charge density wave (CDW). A naive
calculation shows that diamagnetic currents cannot drive rotation of the CDW,
with a clear picture of the cancellation mechanism.
