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