depends only on the conjugacy class of "u" and generates a correspondence between the irreducible representations of the Weyl group and the pairs ("u", φ) modulo conjugation, called the Springer correspondence. It is known that every irreducible representation of "W" occurs exactly once in the correspondence, although φ may be a non-trivial representation. The Springer correspondence has been described explicitly in all cases by Lusztig, Spaltenstein and Shoji. The correspondence, along with its generalizations due to Lusztig, plays a key role in Lusztig's classification of the irreducible representations of finite groups of Lie type.