  We study the continuous map induced on spectra by a separable extension of
tensor-triangulated categories. We determine the image of this map and relate
the cardinality of its fibers to the degree of the extension. We then prove a
weak form of descent, "up-to-nilpotence", which allows us to generalize
Quillen's Stratification Theorem to equivariant derived categories.

Category Theory;Algebraic Geometry;Algebraic Topology;Representation Theory