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