  We prove that a Lebesgue measure-preserving linked-twist map defined in the
plane is metrically isomorphic to a Bernoulli shift (and thus strongly mixing).
This is the first such result for an explicitly defined linked-twist map on a
manifold other than the two-torus. Our work builds on that of Wojtkowski who
established an ergodic partition for this example using an invariant cone-field
in the tangent space.
