FUNCTION:  Index - Index of connection for a crystallographic root system
CALLING SEQUENCE:  Index(R);,    
PARAMETERS:  R = a crystallographic root system data Structure
SYNOPSIS:   
  The Index of connection of a crystallographic root system R is the
  Index of the root lattice of R in the weight lattice of R. Equivalently,
  it is the determinant of the Cartan matrix. It can also be obtained as
  CharPoly(w,R,1), where w is a Coxeter element. If R is irreducible, it
  is also 1 + the number of 1's in the root coordinates of HighestRoot(R).

  If the given root system is not crystallographic, an error is generated. 
     
  For a description of root system data Structures, see Coxeter[Structure].
EXAMPLES:   ,  Index(D4);                 yields     4 
  Index([e1-e2,2*e2]);       yields     2
SEE ALSO:  CartanMatrix, CharPoly, HighestRoot, RootCoords, Structure):
