Naked Quadruple in Sudoku

Naked Quadruple Technique

The Naked Quadruple expands on the logic of Naked Triples but uses four cells and four digits within a unit (row, column, or block). If four cells in a unit collectively hold exactly four unique candidates, those digits must fill one cell each and are eliminated from other cells in the same unit.

Key Rules:

• No cell needs all four candidates, nor must every digit appear in all four cells.
• The total candidates across the four cells must exactly match the four digits.

Example 1: Naked Quadruple in Row 5 (R5)

• Cells: R5C4, R5C5, R5C6, R5C7.
• Candidates: 1, 3, 6, 9 (marked in red).
• Elimination: Remove 1, 3, 6, and 9 from other cells in R5 (e.g., R5C1, R5C9).

Logic: Since these four digits must occupy the four green cells, they cannot appear elsewhere in R5.

Example 2: Naked Quadruple in Block 9 (B9)

• Cells: R8C7, R8C8, R8C9, R9C9.
• Candidates: 1, 2, 5, 7 (marked in red).
• Elimination: Remove 1, 2, 5, and 7 from other cells in B9 (e.g., R7C7, R9C8).

Logic: These digits are confined to the four green cells, excluding them from the rest of B9.