GridWits
Extreme tier Technique 20 of 21 Smart Hint: Skyscrapers+

Jellyfish

A height's candidate cells across four rows (or columns) line up in the same four columns (or rows) — eliminate it everywhere else in those columns or rows.

How it works

  1. 1The same fish one size larger again: four rows, four columns. Follow height 1 down the top four rows.
  2. 2Row 1 allows it in columns 1-2, row 2 in columns 2-3, row 3 in columns 3-4, row 4 in columns 1 and 4. Four rows, and between them only columns 1, 2, 3 and 4.
  3. 3Four rows each need their 1, and only those four columns can provide one — so all four columns are used up before the bottom row gets a look in.
  4. 4Strike 1 from the bottom row's first four cells. Its 1 must be in the last column.
  5. 5This is the top of the fish ladder: a five-row fish on a 5x5 board would just be restating that every row needs a 1.
1 3 1 4 1 2 1 5 1 4 1 3 1 5 1 2 1 2 3 1 3 4 1 4 5 1 2 5
  • Height ruled out
  • Relationship — The arrow shows which cells support the deduction.
  • Conclusion — The final arrow lands beside the proved or ruled-out height.
Next in the ladder Cross-Line Forcing →

Same as Cross-Line Consistency, but each arrangement is also followed through: fill in every height it forces outright, and rule it out if that leaves some other row or column unfinishable.