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