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