Sudoku guides

Straight answers about the parts of sudoku that are genuinely hard to explain. Written to be useful whether or not you ever install the app.

• What an X-Wing means in sudoku

  The pattern, why the elimination is forced rather than likely, how to spot it without hunting, and how Swordfish is the same idea one size larger.

• Naked pairs and hidden pairs, explained

  What a naked pair removes, what a hidden pair removes, why they are opposites, and the mistake that makes players think a hidden pair does nothing.

• Why does my sudoku have more than one solution?

  The four real causes, the rectangle pattern that guarantees a second solution, why 17 is the famous number, and what a solver actually checks.