X ( 2 , 7 , 3 , 8 ) X ( 4 , 2 , 5 , 1 ) X ( 6 , 3 , 7 , 4 ) X ( 8 , 6 , 1 , 5 ) {\displaystyle X(2,7,3,8)X(4,2,5,1)X(6,3,7,4)X(8,6,1,5)}