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Kraken |
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A Kraken is a finned fish where the fin is the starting point of a Forcing Chain. If the forcing chain has a weak connection into any of the potential eliminations of the unfinned fish, that candidate can be eliminated.
Consider the example on this page. We have a finned swordfish of 5's highlighted in yellow and blue, where the 5 in blue is the fin. This 5 is weakly connected to the 3 in the same cell, which is strongly connected to the 3 up above, which is weakly connected to the 7 in the same cell, which is strongly connected to the 7 to the left, which is weakly connected to the 7 above, which is strongly connected to the 7 to the right, which is weakly connected in the same cell to the 5 highlighted in green. Because this 5 is one of the values that would be eliminated if the swordfish (unfinned) were true, it can be eliminated.
Consider the following logic. If the 5 in blue were false, then the swordfish would be true eliminating all other candidates in columns 3, 4 and 9, including the 5 highlighted in gree. If, however, the 5 in blue were true, then following the logic of a forcing chain the 5 in green could again be eliminated. So we see that either way the 5 in green can be removed.
Note that the first connection out of the fin must be a weak connection, and that the connections must alternate between weak and strong.
Krakens are similar to Chained Sets, except that a finned fish is used instead of an Almost Linked Set.
Sudoku Snake gives Krakens a skill value of 6000.
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