  It is reported that when a light beam travels through a slab of left-handed
medium in the air, the lateral shift of the transmitted beam can be negative as
well as positive. The necessary condition for the lateral shift to be positive
is given. The validity of the stationary-phase approach is demonstrated by
numerical simulations for a Gaussian-shaped beam. A restriction to the slab's
thickness is provided that is necessary for the beam to retain its profile in
the traveling. It is shown that the lateral shift of the reflected beam is
equal to that of the transmitted beam in the symmetric configuration.
