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