FUNCTION: LieTools/Dg
USAGE: Dg(i,gpoly)
SYNOPSIS: Dg(i,gpoly) computes the action of the 1st-order differential operator 
  corresponding to the action of a basis element g[i] in g on a polynomial gpoly
  is S(g).
CAVEATS: requires a previously initialized global Lie algebra environment.
  (See LieTools[gSetup].)
EXAMPLE: 
> LieTools[gSetup](G,2);
Setting up Gtype = G   rnk = 2
> LieTools[Dg](1,g[14]^2);

                     -2 g[14] g[7] - 4 g[14] g[8]


SEE ALSO: LieTools[gActionSg]
