Lesson 13

Naked Quad

The rule

Four cells in the same row, column, or box whose candidates together cover only four numbers keep those numbers for themselves.

Step by step

1. In this row, the candidates in these four cells are limited to 1, 2, 3, 4.
2. These four cells together must contain 1, 2, 3, 4, so we can remove the marked candidates from the other cells in this row.
3. Done! We've cleaned up the extra candidates and the board is simpler now.