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