The case notes
Reject a line value that empties the next box
This region sum line crosses a box border. One cell is in the left box; two are in the next. Their segment totals must match. Watch a worked example, then try the idea in a puzzle.
Put it into practice
One cell = two-cell sum
This region sum line crosses a box border. One cell is in the left box; two are in the next. Their segment totals must match.
The box needs 3 on the line
Look at the box on the right. The three given threes outside rule three out of its other seven cells. Its own three must be in one of these two line cells.
Try 6 → {1, 5} or {2, 4}
Try six in the single cell on the left. The two cells across the border would also sum to six. Since they share a row, they must be one and five, or two and four.
No 3 in the box? Remove 6.
Neither pair contains three. That would leave the box without its three. So six cannot sit in the single-cell segment.
Read the transcript
This region sum line crosses a box border. One cell is in the left box; two are in the next. Their segment totals must match. Look at the box on the right. The three given threes outside rule three out of its other seven cells. Its own three must be in one of these two line cells. Try six in the single cell on the left. The two cells across the border would also sum to six. Since they share a row, they must be one and five, or two and four. Neither pair contains three. That would leave the box without its three. So six cannot sit in the single-cell segment.
