Mirrored from Sudopedia, the Free Sudoku Reference Guide
The following fish diagram shows only one of the many possible variations:
The defining set contains rows 1, 5 and 9 and column 5. The secondary set contains columns 2 and 8 and boxes 2 and 8. All candidates for digit X in the defining set are confined to the secondary set. There are no candidates located in more than one defining house. This pattern can cause a maximum of 20 eliminations.