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