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Fish Patterns
  A Fish is a group of candidates of a single value that fall within primary and secondary units. In other words, X number of primary units where the candidates in those units are found only within X number of secondary units. The names for the fish patterns depend on their magnitude, or this number for X, and are as follows:

1X1 - Hidden Single
2X2 - X Wing
3X3 - Swordfish
4X4 - Jellyfish
5X5 - Squirmbag
6X6 - Whale
7X7 - Leviathan

  A fish is considered normal if the primary units are all rows or columns and the secondary units are all columns or rows. Any other formation is considered mutant. Unless a fish is mutant then because of the 9X9 sudoku arrangement, a fish of 9-X magnitude or less in the opposite direction must always exist. For example, if there is a Squirmbag (5X5) in the rows, then there must a Jellyfish (4X4) or less in the columns. (9-5=4). Similarly, if there is a swordfish in the rows, then there must be a Whale or less in the columns. For this reason is it moot to consider anything in magnitude higher than a jellyfish unless it is mutant.

  Due to the high amounts of processor time required to spot them, Sudoku Snake currently does not look for or consider mutant fish higher than Mutant Jellyfish, but is considering adding them into future versions.

Elders of Genova
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