Techniques / Single Digit Patterns
Skyscraper
Two rows (or columns) where a digit has two candidates each and they line up on one side.
Take a digit that has exactly two candidates in each of two rows. If one pair of these candidates is in the same column (the base), the other two (the roofs) are in different columns. One of the two roofs must be the digit, no matter how the base resolves.
So any cell that sees both roofs cannot be that digit. Remove the digit from all such cells.
Notation
Skyscraper: 5 can be removed from r9c6.
pattern removed
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