Techniques · Expert
X-wing
An X-wing is one digit that forms a rectangle. In two rows, the digit has only two possible columns, and they are the same two columns in both rows. The digit has to occupy opposite corners of that rectangle, so it is eliminated from the rest of those two columns.
Drawn the other way, two columns each hold the digit in the same two rows, and the rest of those rows loses it. Pointing and claiming are the one-house version of this lock. The X-wing is the same lock across two houses.
When it shows up
X-wings are Expert. Not Easy and Hard never require one.
The 1,483 archived NYT puzzles never need an X-wing. Their hardest steps stop at triples.
See it on a real puzzle
The marks are the candidates left when this is the next step in the solve. Step through it: the pattern, what leaves, and what that forces.
See the pattern
Look at the 8s in these two columns.