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Fill in each square in this grid with a digit from 1 to 9. The sum of the digits in each row or column will equal the little number to the left or above it. See the two-box row at the upper left with a 6 to the left of it? The sum of the digits in those two squares will be 6, and neither digit will be the same (i.e., no two 3’s). A row or column ends at a black square, so the three-square row in the upper-middle with a 6 to its left may have digits in common with the 6-row to the left of it; they’re considered different rows because they’re separated by a black square. Down columns work the same way. Now solve!