This revised post illustrates how the n base, n cover rule is applied in the mutant fish economy. An example of a valid finned fish is followed by a homework assignment checkpointed by a forward link to the Hodoku review of 2015.
We start with a checkpoint on your homework, where you read the victims to reconstruct both the guilty mutant fish and equivalent, equally murderous grouped nice loop. Here is the crime scene.
In the Sudoku9981 mutant swordfish, the base units fail the mutant fish rule because they violate the “disjointly covered” specification. It’s OK because the commodity to be shared are the positions for true candidates along the rows. The base positions are just so easy to cover.
This violation is no problem for the nice loop, but exactly what is it we don’t know about the mutant victims? Going through our “proof”, we could have two “base” units sharing the same true candidate, and a cover of a true X not in a base unit.
Moving on to finned mutant, or Franken, fish, exactly where is the fin? Falling back on the regular fish model, the fin is an extra base candidate that can supply the missing ingredient that a victim of the fish would otherwise take. In finned fish of n rows, the fin is an extra candidate in a fish row that replaces a candidate seen by an outside candidate in one of the n columns of the fish.
Translating to mutant fish, the fin is an extra, uncovered base candidate that would replace a candidate in a base unit seen by an outside candidate in a cover set. In Sudoku Snake’s finned mutant from on www.sudokusnake.com that is X-paneled here, base units have candidates in three covered positions. The fin in an extra position takes the place of r7c9 in the SE box if it is removed by possible victims in r9. But r9c46 are finned fish victims because they see the fin, preventing it from doing the replacement.
Also, the fin is a spoiler candidate for the mutant fish. If it is true, a potential victim that sees it is false. If it is false, the potential victim becomes the actual victim of the repaired fish.
The kraken analysis of this finned fish is easy. By simple winks and forcing chains, the other potential victims confirm the fin by removing opposing candidates in SE and r8, preventing the fish from removing them.
This finned mutant could be spotted by noting the line and two boxes confined to three columns, except for a single candidate.
As a second example of finned mutant fish, here is a finned Franken Swordfish identified by Hoduku on the same candidates as the mutant jellyfish cited in the last post, at http://hodoku.sourceforge.net/en/tech_fishc.php . A Franken fish, according to Hodoku, is a mutant fish with one base or cover box. This one has two base columns and a fin at r5c7. That’s all you need to know. There are three cover lines. Just mark the base and cover sets, and do the kraken analysis. Your checkpoint is in the post Hodoku Franken Fish of 12/22/15
Next we look at a very strange mutant fish, if it is a fish, which I doubt.