GridWits
Easy tier Technique 2 of 46 Used by Smart Hint

Hidden Single

A digit has only one possible cell left in a row, column, or box, even though that cell has other candidates too.

How it works

  1. 1Scan this box for digit 7: only D4 still lists it — every other empty cell has ruled 7 out.
  2. 2Nothing cheaper is available: no cell here is down to a single candidate, and every other missing digit still has two homes or more.
  3. 3D4 carries 1, 4 and 9 as well, so it isn't a Naked Single — but 7 has nowhere else to go in the box. Place it.

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 4 7 9 2 1 6 9 5 1 9 3 4 6 8 1 4 6 9
  • Where the conclusion lands
Next in the ladder Pointing Pair/Triple →

All of a digit's candidates in a box line up in one row or column, so it can be eliminated from the rest of that line.