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Points. A Skyscraper is a single-digit solving technique that uses two parallel strong links weakly connected at one end. The connection is at the "base" of a Skyscraper that is oriented vertically with the link at the bottom. A Skyscraper is a type of Turbot Fish, or length 5 loop. With 2 strong links and 3 cover links, itis  chain-like with a rank of  1.


Skyscraper, vertical. The first example is a vertical skyscraper, which works like a very simple chain. The cover link regions are highlighted showing the overlap region between box 1 and row 2.


In terms of implications:


9r2c7  => r2c3<>9

r2c7<>9 => 9r8c7 => r8c2<>9 => 9r2c2 =>  r2c3<>9


In terms of truths and covers, 2 truths + 3 covers imply any candidate covered by two links can be eliminated. Thus r2c3<>9.  The elimination region includes all three cells in the intersection of box 1 with row 2.



Skyscraper with double ends. This example shows another vertical skyscraper that eliminates two candidates, one elimination uses box 1 and row 2, the other elimination uses box 3 and row 2.

Horizontal Skyscraper. This example shows another horizontal skyscraper. A horizontal skyscraper is logically equivalent to a vertical skyscraper.