Havard wrote:It has probably to do with the fact that when I identify an x-wing or a swordfish, I look to eliminate all candidates that the end-points of the strong links has in common (the ones they both see), and hence the elimination you pointed out I (and my solver) did long before I knew anything about fins.

This is probably sufficient for your self, but for helper programs & giving pointers, it is not.

Classic fishes of a size of N, should have candidates in N rows & N columns & eliminate in Lines, you can't describe your example as an x-wing.

Nobody is inventing the wheel, we are trying to get hold of what this technique is capable of.

At this moment for manual solver & programmer IMO it stands as follows.

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`1. Attempt to construct the framework of an N*N fish using any combination of true & virtual vertices. (a number of true vertices is needed of course...a minimum of N candidates to cover N non-elimination lines & N-1 elimination lines [to be verified])`

2. If there exists a number of candidates (fins) preventing this formation which are all sharing 1 box with A vertix (true or virtual) then...

Eliminate any candidate in that box which is in the line of elimination of A vertix (true or virtual).

3. if a line of elimination in finned fish is constructed from virtual vertices only...then

true vertices retain classic fish-style elimination, & a quantum cell of the candidate is created from ALL fin cells.

I consider that an advanced technique, but with practice it should be easy to construct & has proved to be very powerful.

The above is true for finned x-wings & swordfishes, & it holds even IF simpler elimination techniques are present.

I haven't tested it on finned Jellyfishes yet.

Tarek