Skyscraper: two towers, one roof
The Skyscraper is a single-digit technique. Two rows in which a digit appears exactly twice and shares one column form two towers on a common base. The two free ends give you a safe elimination. Click through an example below.
Interactive example
Click ‘Step’ to see the pattern and the elimination.
Try it: Skyscraper
How the Skyscraper works
Find a digit that appears exactly twice as a candidate in two rows and shares one common column, which is the base. The two remaining ends are the roof. Since each of the two rows carries the digit in exactly one end and both rows meet at the base, at least one of the two roof ends must be the digit. Any cell that sees both roof ends at once therefore cannot hold the digit and it is removed there. The same works with the roles of rows and columns swapped.