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