Sudoku Rules

Easy

Normal

Hard

Expert

Master

Sudoku Techniques: Naked Quad

Naked Quad

Look for four cells containing the same four candidates

Sudoku Techniques: Hidden Quad

Hidden Quad

Find a quad hidden in the unit

Sudoku Techniques: XYZ-Wing

XYZ-Wing

An advanced version of XY-Wing with an additional candidate

Sudoku Techniques: WXYZ-Wing

WXYZ-Wing

An extension of the previous wings using four cells

Sudoku Techniques: Skyscraper

Skyscraper

Two columns connected by a shared candidate