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Sudoku Rules
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Chains & Colours
Naked Quad
Look for four cells containing the same four candidates
Hidden Quad
Find a quad hidden in the unit
XYZ-Wing
An advanced version of XY-Wing with an additional candidate
WXYZ-Wing
An extension of the previous wings using four cells
Skyscraper
Two columns connected by a shared candidate
2-String Kite
A very short single-digit chain where one end must be true
Turbot Crane
The third type of short chain involving a single digit