  Snell's law states that the quantity $n\sin\theta$ is unchanged in refraction
of light passing from one medium to another. We inquire whether this is true in
the general case where the speed of light varies continuously within a medium.
It turns out to be an instructive exercise in application of Snell's law and
Fermat's principle. It also provides good pedagogical problems in calculus of
variations to deal with the subtleties of a variable domain of integration and
inclusion of constraints. The final result of these exercises is that, contrary
to an initial expectation, the answer to the question in the title is negative.
