GridWits
Hard tier Technique 19 of 31 Used by Smart Hint

Naked Quad

Four cells in a house between them using only four candidates lock those digits away from the rest.

How it works

  1. 1Find four cells in one house whose combined candidates are exactly four digits.
  2. 2They consume all four between them, in some order.
  3. 3Strike those four digits from every other cell in the house.
Next in the ladder Hidden Quad →

Four digits confined to the same four cells clear those cells of everything else.