z1 := (1,2)(3,7)(4,8)(5,9)(6,10)(11,18)(12,19)(13,20)(14,15)(16,21)(17,22)(23,
     31)(24,32)(25,33)(26,34)(27,35)(28,36)(29,37)(30,38)(39,49)(40,45)(41,50)
     (42,47)(43,51)(44,52)(46,53)(48,54)(55,56);