Skyscraper
When two lines share one base and leave two roof candidates.
Explanation
If a candidate appears twice in two rows and the rows share one column, at least one of the two non-shared roof cells must contain that candidate. Any cell that sees both roofs can remove it. The same pattern works with rows and columns swapped.
Practice tip
Scan one candidate at a time after X-Wing. Look for two strong pairs that share one endpoint.
Example steps
- Find two rows with the same candidate in exactly two cells.
- Confirm the rows share one column as the base.
- Remove the candidate from cells that see both roof cells.