GridWits
Expert tier Technique 13 of 20 Reference only

Hidden Quad

Four guaranteed digits only fit in the same four cells of a run — strip those cells down to just those four.

The solver does not attempt this technique, so Smart Hint will never suggest it. It is documented because you may still want to spot it yourself.

How it works

  1. 1Six cells summing to 37 means three digits are missing from 1-9 and they add to 8 — only {1, 2, 5} or {1, 3, 4}.
  2. 2So the run is either {3, 4, 6, 7, 8, 9} or {2, 5, 6, 7, 8, 9}: a 6, a 7, an 8 and a 9 are guaranteed either way.
  3. 3None of those four fit in the first two cells, so they must fill the last four — one apiece.
  4. 4Strike the leftover small candidate from each of those four cells.
37 2 3 4 5 2 3 4 5 2 6 7 8 3 6 7 9 4 7 8 9 5 6 8 9
  • Cells that establish the pattern
  • Where the conclusion lands
  • Digit ruled out
Next in the ladder Arrangement Check (Wide) →

The same fit-the-cells check on a run offering four to six combinations — enough that you have to write them out and cross off rather than compare them in your head.