X ( 2 , 7 , 3 , 8 ) X ( 4 , 11 , 5 , 12 ) X ( 6 , 18 , 1 , 17 ) X ( 8 , 1 , 9 , 2 ) X ( 10 , 16 , 11 , 15 ) X ( 12 , 3 , 13 , 4 ) X ( 13 , 20 , 14 , 21 ) X ( 16 , 6 , 17 , 5 ) X ( 18 , 10 , 19 , 9 ) X ( 19 , 22 , 20 , 7 ) X ( 21 , 14 , 22 , 15 ) {\displaystyle X(2,7,3,8)X(4,11,5,12)X(6,18,1,17)X(8,1,9,2)X(10,16,11,15)X(12,3,13,4)X(13,20,14,21)X(16,6,17,5)X(18,10,19,9)X(19,22,20,7)X(21,14,22,15)}