  Let g be a complex simple Lie algebra and let V be a finite dimensional U(g)
module. A relative Yangian is defined with respect to this pair.
  According to recent work of Khoroshkin and Nazarov the finite dimensional
simple modules of the Yangians for g = sl(n) or the twisted Yangians for g =
sp(2n); so(n) are described by the simple modules of relative Yangians for some
V using the appropriate simple Lie algebra g. Here a classification of the
simple modules of a relative Yangian is obtained simply and briefly as an
advanced exercise in Frobenius reciprocity inspired by a Bernstein- Gelfand
equivalence of categories. An unexpected fact is that the dimension of these
modules are determined by the Kazhdan-Lusztig polynomials and conversely the
latter are described in terms of dimensions of certain extension groups
associated to finite dimensional modules of relative Yangians.
