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