Duplicate Trap
Hard
Used by Smart Hint
Keeping this cell would reject every other copy of its number in its row and column at once — and that burst of rejections would seal part of the board off from the rest. So the cell is rejected instead.
- Rejected
- Cells that establish the pattern
- Where the conclusion lands
How it works
- Suppose the corner 7 were kept. Its number can't repeat among kept cells in its row or column, so the 7 beside it AND the 7 below it would both have to be rejected, immediately.
- That leaves the corner surrounded by rejected cells on both its sides — cut off from every other kept cell, which the connection rule forbids.
- So the corner can't be kept: reject it.