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