Skyscraper
ExpertTake one digit and two rows where it has exactly two places each. If one end of each row is in the same column (the base) and the other two ends are not, those two ends are the tops of a skyscraper. One of them must be the digit, so a cell that sees both tops can’t be it.
How to spot it
- Pick one digit and find rows (or columns) where it has exactly two places.
- Find two whose ends line up in one column but not in the other.
- Remove the digit from cells that see both unaligned ends.
Why it works
The two aligned ends can’t both be the digit: they share a column. So at least one row places its digit at its other end, the top, and whatever sees both tops loses the digit.
Example
1
9
4
5
3
5
4
2
3
1
9
6
3
2
9
5
4
7
9
8
6
2
7
9
5
3
2
9
3
5
9
7
2
1
7
5
1
2
9
6
3
2
1
9
6
3
7
4
8
5
Look at the 8s in row 2 and row 8.
Common mistakes
- Taking two rows whose ends line up in both columns: that is an X-wing, with other eliminations.
- Removing the digit from cells that see only one top.