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