b21 := (1,2,3)(4,6,7)(5,8,9)(10,13,14)(11,15,16)(12,17,18)(19,25,26)(20,27,28)
     (21,23,29)(22,30,31)(24,32,33)(35,39,40)(36,41,42)(37,43,44)(38,45,46)
     (47,51,52)(48,49,53)(50,54,55);