Key Points
  • Both techniques eliminate candidates by proving which cells cannot hold a digit
  • Skyscraper uses conjugate pairs in two rows (or columns) to make eliminations
  • XY-Wing uses three cells with two candidates each to eliminate a third candidate elsewhere
  • These patterns typically appear when Easy techniques (pairs, singles) are exhausted
  • Spotting these in your pencil marks turns a stalled Hard puzzle into progress

The Skyscraper Pattern

A Skyscraper involves a single digit appearing in exactly two cells in each of two different rows (or columns). If those pairs share a column (or row), you can eliminate that digit from other cells that see both "top cells" of the pattern.

How to spot it: Look for a digit with exactly two candidates in two rows. If those pairs are in the same two columns, you have an X-Wing (which eliminates the digit from those entire columns). If they are in different columns but one column is shared, you have a Skyscraper — and you can eliminate the digit from any cell that sees both unshared endpoints.

The XY-Wing Pattern

An XY-Wing uses three cells called the pivot and two pincers:

  • The pivot has exactly two candidates: XY
  • One pincer (in the same row, column, or box as the pivot) has candidates XZ
  • The other pincer (also sharing a unit with the pivot) has candidates YZ

No matter which value the pivot takes (X or Y), one of the two pincers must be Z. Therefore, any cell that sees both pincers cannot be Z — and Z can be eliminated from it.

Why These Techniques Work

Both patterns use the same underlying logic: a chain of either-or relationships. If cell A is not the digit, then cell B must be. If cell B is not the digit, then cell C must be. Any cell that would conflict with all possible chain outcomes can have the digit eliminated.

When to Look for Them

Look for Skyscrapers and XY-Wings when you have completely applied Naked/Hidden Singles and Pairs but the puzzle is still stalled. They are most common in Hard and Expert puzzles. The techniques library has visual worked examples of both patterns with annotated grids.