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Death Blossom |
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To understand what a death blossom is, you have to know what an Almost Linked Set is (or ALS), which is basically a group of candidates that is one candidate shy of being a subset (naked or hidden). In a death blossom there is one cell, called the stem cell, that has only two candidates. One candidate shares a unit with the fin of one ALS, and the other candidate shares a unit with the fin of another ALS. Then, if both ALS's cause the elimination of a single candidate, then that candidate can be eliminated, because either value of the stem cell will eliminate it.
Consider the example on this page. The stem cell is highlighted in blue with a 1 and an 8. One ALS is highlighted in yellow in the 5th column, and the other ALS is highlighted in yellow in the 5th row. If the stem cell is a 1, then the ALS in the 5th column becomes a naked subset and eliminates the 5 in the green cell. If the stem cell is an 8, then the ALS in the 5th row becomes a naked subset and also eliminates the 5 in the green cell.
Note, if you haven't yet, that if all of a candidate in a set are found in a single other unit, you can eliminate all others of that candidate in that separate unit. For instance, in the example on this page, if the 8 is eliminated from the 5th row, then it becomes a set where all the 5's happen to be in the middle box. Thus, the 5 in the green cell would be eliminated. This concept is only noteworthy in ALS's, because in standard sets it is swallowed up by the simpler techniques of pointing and claiming. The naked subset eliminates all others of its values from the unit, and thus the remaining 5's in the entire unit are in the same box and become a matter of claiming, which has the same end result.
A death blossom usually only deals with naked ALS's, since they're generally easy to spot, and always exist wherever there is a hidden ALS. An ALS of only one cell may also occur, creating a form of death blossom, but this is ignored in Sudoku Snake and is allowed to be recognized as a chained set.
Sudoku Snake gives Death Blossoms a skill value of 2200.
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