GridWits
Hard tier Technique 9 of 46 Used by Smart Hint

Naked Quad

Four cells in a unit whose candidates combine to exactly four digits — eliminate those digits elsewhere in the unit.

How it works

  1. 1A3, C3, E3 and F3 draw only from {1, 3, 6, 7} between them — a Naked Quad, with no cell holding all four.
  2. 2Row 3 has eight empty cells, so the four left over spread across five digits: no pair, triple or hidden pair reaches these marks first.
  3. 3The quad's digits are locked into its four cells, so they leave the rest of the row — H3 loses 1 and 3, I3 loses its 7.

Play a Sudoku that needs this technique →

A 1 B 2 C 3 D 4 E 5 F 6 G 7 H 8 I 9 1 3 9 3 6 2 4 5 8 1 7 6 7 5 8 1 3 4 5 2 5 7 8 1 3 6 7 1 3 6 7 1 3 6 7 1 3 6 7 1 3 7
  • Cells that establish the pattern
  • Where the conclusion lands
  • Candidate ruled out
Next in the ladder Hidden Quad →

Four digits confined to the same four cells in a unit — strip those cells down to just those four digits.