b21 := (1,2,3)(4,6,7)(5,8,9)(10,14,15)(11,16,17)(12,18,19)(13,20,21)(22,23,28)
     (24,29,25)(27,30,31)(32,36,37)(33,38,39)(34,40,41)(35,42,43)(44,48,49)
     (46,47,50);