GridWits
Hard tier Technique 8 of 11 Used by Smart Hint

Don't Split the Board

All kept cells must stay connected — a cell whose rejection would cut the board into two separate regions has to be kept.

How it works

  1. 1Two cells are rejected — the 3 in the top row and the 3 starting the third row — and every cell touching them is already kept, so the basic rules have nothing left to add.
  2. 2That leaves a pocket in the top-left: three cells whose only route to the rest of the board runs through the single cell diagonally in from the corner.
  3. 3Reject that one cell too and those three become an island of kept cells that can never rejoin the others, which the connection rule forbids.
  4. 4None of the three is trapped on its own, so nothing local gives this away — you have to trace the route out. The cell is kept.
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  • Kept
  • Rejected
  • Cells that establish the pattern
  • Where the conclusion lands
Next in the ladder Duplicate Trap →

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.