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