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