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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 given just to the left or above it. See the four-box row in the upper left with a 27 to the left of it? The sum of the digits in those four squares will be 27, and none of the digits will be the same. A row or column ends at a black square, so the four-square row in the upper-right with a 28 to the left of it may or may not have digits in common with the 27-row to its left; they’re considered different rows because they’re separated by a black square. Down columns work the same way. It’s kinda psychotic!