b21 := (1,2,3)(4,6,7)(5,8,9)(10,13,14)(11,15,16)(12,17,18)(19,24,25)(20,26,27)
     (21,28,29)(22,30,31)(23,32,33)(34,40,41)(35,42,36)(37,43,44)(39,45,46)
     (47,51,52)(48,50,53)(49,54,55);