Sudoku HowTo

# Finned X Wing and Finned Fishy Things

As the name suggests this strategy works on a candidate pattern that is almost an X Wing or other Fishy Thing but has an extra piece to consider. This extra piece is usually referred to as the fin of sometimes the fillet.

The Fin is extra cells in a row or column containing the candidate being considered with all the extra cells contained in a single box.

A Finned Fishy Thing only allows the elimination of candidates from cells that are in the same box as the fin and would have had candidates eliminated if the Fishy Thing did not have the fin.
Figure 1 shows a Finned X Wing pattern on the value 3 in columns 2 and 7. This would be a real X Wing pattern if the value 3 was not a valid candidate in the green cell in column 7. A fin may be more than one cell but all the cells in the fin have to be in the same box. This fin is valid because there are no cells in column 7 containing the value 3 that are not in the X Wing pattern or not in the box containing the fin (Box 6 in this case).

With a Finned X Wing pattern there are two possible solutions. The value 3 will eventually be placed in one of the fin cells (In this case the single green cell) or, if the 3 is not placed in one of the fin cells the X Wing pattern would be valid. In either case the value 3 can be eliminated from cells in the box containing the fin that would have been eliminated if the fin did not exist.

Having the fin on this X Wing does not allow the elimination of the value 3 from the yellow cells that would have been possible if it was a real X Wing.
Figure 2 shows another example of a Finned X Wing pattern on the value 7 that happens to be in the same puzzle as Figure 1. In this case there are two cells in the fin. Note the fin is still completely contained in a box.

Either the 7 has to be placed in one of the green cells or the the X Wing pattern shown as blue cells will be valid. Either of these two possibilities will remove the 7 from the grey cell.
Figure 3 shows an example of a Finned Swordfish on the value 3 in the same puzzle as Figures 1 and 2. Once again the two possible results are, the value 3 gets placed in the green cell, or the Swordfish pattern shown by the blue cells is valid.

Either way the 3 will be eliminated from the grey cell.
And just because it is there, the same puzzle contains a Finned JellyFish on the value 3. The value 3 will either be placed in the green cell or the JellyFish pattern will be valid.

Either way the value 3 will be eliminated from the grey cell.

4 October 2021
by George
RE: Comments and feedback for fishyThingsWithFins

Please do not comment on my message.
4 October 2021
by George
RE: Comments and feedback for fishyThingsWithFins

In fig.3 if 3 is not in place 7-3, why it is still swordfish? In line 7, it will be only one 3. So it cannot be a sword fish formation.

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Acknowledgments

I would like to acknowledge these sites referenced for strategy ideas and solving techniques.

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