Learn
One technique per lesson, shown on a real grid.
Easy
Medium
- Naked singleSometimes a cell can hold only one digit: the eight others are already in its row, its column or its box.
- PointingWhen, inside a box, every place left for a digit lies in the same row (or column), the digit of that box is on that line.
- ClaimingWhen, along a row (or column), every place left for a digit lies inside the same box, the digit of that line is in that box.
Hard
- Naked pairTwo cells of the same row, column or box that can only hold the same two digits share them: one cell gets each.
- Hidden pairWhen two digits can each go in only the same two cells of a row, a column or a box, those two cells hold those two digits.
- Naked tripleThree cells of the same row, column or box that, between them, can only hold the same three digits take those three digits.
- Hidden tripleWhen three digits can only go in the same three cells of a row, a column or a box, those cells hold those three digits.
Expert
- X-wingTake one digit.
- SkyscraperTake one digit and two rows where it has exactly two places each.
- 2-string kiteTake one digit, a row where it has exactly two places and a column where it has exactly two places.
- XY-wingAn XY-wing is three cells with two candidates each.
- XYZ-wingAn XYZ-wing is an XY-wing whose pivot has a third candidate: the pivot holds XYZ, and it sees two pincers holding XZ and YZ.
- W-wingA W-wing starts with two cells holding the same pair, XY, that don’t see each other.
- SwordfishA swordfish is an X-wing with three rows.
- Naked quadFour cells of the same row, column or box that, between them, can only hold the same four digits take those four digits.
- Hidden quadWhen four digits can only go in the same four cells of a row, a column or a box, those cells hold those four digits.
- JellyfishA jellyfish is the next fish after the swordfish: four rows where one digit’s places all fall in the same four columns.