FUNCTION:  Weights - fundamental Weights of a root system,    
CALLING SEQUENCE:  Weights(R);,    
PARAMETERS:  R = a root system data Structure,SYNOPSIS:   
  Weights(R) returns the list of fundamental Weights for R.
  If r_1,...,r_n are the simple roots of R, then the i-th fundamental
  weight is the unique vector v_i in the span of Base(R) such that
                  Iprod(v_i,Co(r_j)) = Kronecker_Delta(i,j),
  where Co(r) = 2*r/Iprod(r,r) denotes the co-root corresponding to r.
  For a description of root system data Structures, see Coxeter[Structure].
EXAMPLES:   
  Weights(G2);               yields          [-e1+e3,-e2-e1+2*e3],    
SEE ALSO:  Rho, WeightCoords, Coxeter[Base], Coxeter[Iprod],
           Coxeter[Structure]):
