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