FUNCTION: LieTools/InvSymMap
USAGE: InvSymMap(ugpoly)
SYNOPSIS: InvSymMap(ugpoly) will find the pre-image of a element
  ugpoly of U(g) under the symmetrizer map S(g) -> U(g).
CAVEATS: requires a previously initialized global Lie algebra environment.
  (See LieTools[gSetup].)
EXAMPLE: 
gSetup(G,2):Setting up Gtype = G   rnk = 2
> X := u(g[1],g[14])+u(g[14],g[1])+u(g[2],g[13])+u(g[13],g[2]);

  X := u(g[1], g[14]) + u(g[14], g[1]) + u(g[2], g[13])

         + u(g[13], g[2])

> x := InvSymMap(X);

                   x := 2 g[1] g[14] + 2 g[2] g[13]

> SymMap(x);

  u(g[1], g[14]) + u(g[14], g[1]) + u(g[2], g[13]) + u(g[13], g[2])

SEE ALSO: LieTools[SymMap], LieTools[NormalOrder]
