นิพจน์ 4: "l" left parenthesis, 2 left parenthesis, "N" "x" minus floor left parenthesis, "N" "x" , right parenthesis , right parenthesis minus 1 , 2 left parenthesis, "N" "y" minus floor left parenthesis, "N" "y" , right parenthesis , right parenthesis minus 1 , right parenthesis less than or equal to absolute value left parenthesis, "r" left parenthesis, StartFraction, 1 Over "N" , EndFraction floor left parenthesis, "N" "x" , right parenthesis , StartFraction, 1 Over "N" , EndFraction floor left parenthesis, "N" "y" , right parenthesis , right parenthesis , right parenthesisl2Nx−floorNx−1,2Ny−floorNy−1≤absr1NfloorNx,1NfloorNy