X ( 1 , 4 , 2 , 5 ) X ( 3 , 8 , 4 , 9 ) X ( 5 , 13 , 6 , 12 ) X ( 7 , 2 , 8 , 3 ) X ( 9 , 19 , 10 , 18 ) X ( 11 , 15 , 12 , 14 ) X ( 13 , 7 , 14 , 6 ) X ( 15 , 20 , 16 , 1 ) X ( 17 , 11 , 18 , 10 ) X ( 19 , 16 , 20 , 17 ) {\displaystyle X(1,4,2,5)X(3,8,4,9)X(5,13,6,12)X(7,2,8,3)X(9,19,10,18)X(11,15,12,14)X(13,7,14,6)X(15,20,16,1)X(17,11,18,10)X(19,16,20,17)}