Skyscraper
Level: Advanced
A single-digit chain technique that links two strong links.
A Skyscraper forms when, for a specific number, two lines each contain that number in exactly two cells, with one end of each aligned in the same column (or row).
Treat the aligned pair as the 'base' — the number must go in one of the two remaining cells. In any cell seen by both of those cells, you can eliminate that number.
It's a classic example of a single-digit chain, often used as an alternative when an X-Wing doesn't apply.
Related Techniques
Intermediate
X-Wing
A rectangle pattern where a number's candidates in two lines fall in exactly the same two cells.
AdvancedXY-Wing
Eliminates a shared number using a candidate chain between a pivot and two wing cells.