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