FUNCTION:  Diagram - Dynkin Diagram of a root system,    
CALLING SEQUENCE:  Diagram(R);,    
PARAMETERS:  R = a root system data Structure,SYNOPSIS:   
  Diagram(R) displays the Dynkin Diagram of the root system R, with the
  nodes numbered according to the ordering of simple roots used by Base(R).
  The displays for G2, H3, H4 and I2[m] are ugly.
  For a description of root system data Structures, see Coxeter[Structure].
EXAMPLES:   ,  Diagram(E8);         yields
                    2,                    |
            1---3---4---5---6---7---8,  Diagram(B3*D4);      yields
                1=<=2---3,                    5
                    |,                4---6---7,    
SEE ALSO:  Base, NameOf, Structure):
