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