FUNCTION: LieTools/SgEvalOnPrNil
USAGE: SgEvalOnPrNil(gpoly);
SYNOPSIS: This routine evaluates a polynomial in S(g) on the nilpositive
  element of the canonical principle TDS.
CAVEATS: requires a previously initialized global Lie algebra environment.
  (See LieTools[gSetup].)
EXAMPLE: 

SEE ALSO: 
