Place the digits 1 to 8 in each row and each column. Each horizontal domino that has both its digits in the first 7 columns forms the coordinates of a digit in the grid: The leftmost member of the pair is its row. The rightmost member of the pair is its column. Its value is the row in which the pair is. For instance, if R4C1 contains 7 and R4C2 contains 5 then R7C5 contains 4.