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