Comparison of the theoretical Snell's law given by (15a) and (15b) (lines) against full numerical computations (points) for a unit-amplitude () spatial soliton at a nonlinear interface () with and when (a) and (b) . Curves below (above) the line are labelled by the right-hand (left-hand) legend and have () so that refraction is internal (external). Note that the numerical datapoints for and are very close together in both panes.