FUNCTION:  Size - Size of a Coxeter group,    
CALLING SEQUENCE:  Size(R);,    
PARAMETERS:  R = a root system data Structure,SYNOPSIS:   
  Size(R) computes the Size of the Coxeter group W(R) by evaluating the
  product of the Degrees of the basic polynomial invariants of W(R).
  For a description of root system data Structures, see Coxeter[Structure].
EXAMPLES:   ,  Size(E8);                yields     696729600,    
SEE ALSO:  Degrees, LengthGF, Orbit_Size, Structure):
