sudokUI › Sudoku techniques › Whale
Whale in sudoku
6-fish · flip side of a smaller fish · how it fits
Digit X has two to six candidates in each of six rows, all lying in the same six columns, or likewise with rows and columns swapped.
Why it works
Each of the six rows places X in a different one of the six columns, so all six columns get their X from these rows. Remove X from all other cells in those columns, or in those rows for the swapped form.
How to spot it
Look at the columns outside the pattern: at most three still need X, and they form smaller fish or singles giving the same eliminations.
Implemented, but never needed: an easier technique always reaches the same result first.
In a puzzle's rating
Each time the solver needs Whale, the puzzle's difficulty rating grows by 470. Its class is Unfair. How the rating works.