FUNCTION: LieTools/UgEvalOnHWV
USAGE: UgEvalOnHWV(upoly,hfw):
SYNOPSIS: UgEvalOnHWV(upoly,hfw) will yield the evaluation of an 
  element upoly in U[g] on a highest weight vector of a Verma module
  with highest weight hfw (expressed in terms of a basis of fundamental
  weights). The result is expressed as element of the enveloping algebra
  U(n-) of the subalgebra n_ generated by the negative root vectors. 
CAVEATS: requires a previously initialized global Lie algebra environment.
  (See LieTools[gSetup].)
EXAMPLE: 
> with(LieTools):
> gSetup(A,1);
Setting up Gtype = A   rnk = 1
> upoly := u(g[1],g[1]);

                        upoly := u(g[1], g[1])

> UgEvalOnHW(u(g[1],g[1]),[2]);

                            u(g[1], g[1])

> UgEvalOnHW(u(g[1],g[2]),[2]);

                              2 u(g[1])

> UgEvalOnHW(u(g[3]),[2]);

                                  0

SEE ALSO: LieTools[VermaNorm]
