Killer Sudoku rules and puzzles

The case notes

Use a box to constrain a crossing Killer cage

This fourteen-cage crosses a box edge. Two of its cells are inside the upper-left box; its third sits outside. The position of nine in that box matters. Watch a worked example, then try the idea in a puzzle.

Put it into practice

A cage crosses the box

This fourteen-cage crosses a box edge. Two of its cells are inside the upper-left box; its third sits outside. The position of nine in that box matters.

The box’s 9 is in the cage

Other nines remove the third row, the first column and the second column of this box. Only these two cells can still hold its nine. Both are inside the cage.

14 − 9 = 5

We do not know which cage cell is nine. We do know the cage contains one. Its total is fourteen, so the other two cells must add to five.

Outside cell: only 1, 2, 3 or 4

Two different positive digits make five as one and four, or two and three. The outside cage cell cannot be six. In fact, it cannot be five or higher.

A box can claim a cage digit

The box did not place nine, but it claimed nine for the cage. That was enough to tighten the cage’s other cells.

Read the transcript

This fourteen-cage crosses a box edge. Two of its cells are inside the upper-left box; its third sits outside. The position of nine in that box matters. Other nines remove the third row, the first column and the second column of this box. Only these two cells can still hold its nine. Both are inside the cage. We do not know which cage cell is nine. We do know the cage contains one. Its total is fourteen, so the other two cells must add to five. Two different positive digits make five as one and four, or two and three. The outside cage cell cannot be six. In fact, it cannot be five or higher. The box did not place nine, but it claimed nine for the cage. That was enough to tighten the cage’s other cells.

Keep following the clues