FUNCTION:  NumRefl - number of Reflections in a Coxeter group,    
CALLING SEQUENCE:  NumRefl(R);,    
PARAMETERS:  R = a root system data Structure,SYNOPSIS:   
  NumRefl(R) returns the number of Reflections in the Coxeter group W(R),
  or equivalently the number of positive roots. The result is obtained by
  evaluating the sum of the Exponents of R.
  For a description of root system data Structures, see Coxeter[Structure].
EXAMPLES:   ,  NumRefl(B3*A3);             yields     15,    
SEE ALSO:  Exponents, PosRoots, Structure):
