X-Wing: lock one digit into a rectangle
An X-Wing uses one digit that appears in exactly the same two columns across two rows, or the same two rows across two columns.
Key idea
Each base row must place the digit once, so both cover columns are occupied by the pattern and the digit is impossible elsewhere in those columns.
See the move, step by step
Build an X-Wing on candidate 7 in rows 1 and 3.
Step 1 of 4
Filter for one digit
Look only at candidate 7 and compare rows with exactly two possible positions.
Step 2 of 4
Confirm both rows align
Rows 1 and 3 place 7 only in columns 1 and 3, forming four aligned corners.
Step 3 of 4
Clear the cover columns
Candidate 7 at R5C1 and R7C3 lies in the cover columns but outside the base rows, so both can be removed.
Step 4 of 4
Keep the four corners
The corners remain unresolved; only the outside candidates disappear.
Try it on today's puzzle
Scan one digit at a time. A rectangle is not enough: all candidates in each selected base row must stay inside the same two cover columns.
Play today