![]() ![]() There's not enough room here to give all of my results, but if you contact me by email, I'd be happy to share what I've done. I implemented the resulting rules using a lookup table in my solver. When I refer to the number of patterns found, I've excluded reflections and rotations of the basic patterns. Summarizing only patterns that give eliminations of internal UR candidates, I found 8 different UR+2 patterns with adjacent guardians, 11 different UR+2 patterns with diagonal guardians, 18 different UR+3 patterns, and 5 different UR+4 patterns. I worked out the truth tables for every possible combination of UR's with 2, 3 or 4 extra candidate cells ("Guardian cells" in my notation) with every possible combination of strong links between the various cells. One day, having nothing better to do, that's exactly what I did. It occurred to me that it would be much simpler just to work out the truth tables for them. The logic for many of them is so convoluted that it made my head spin. I spent many hours going through that post and many others in the same thread. If I'm not mistaken, the one that you refer to as Type 5 is referred to as UR+2D/1SL (not to be confused with UR+2D or UR+2d). ![]() I ran across it while implementing UR's in my own solver last year. It is described on the enjoysudoku forum, along with many other variations of UR's having two extra candidate cells, located diagonally. I believe the new type 5 that you posted (January 2021), has been known for some time. Ivar's example can be found if you turn off 3D Medusa first. This is not allowed so 2 can be removed from the Naked Pair. If 2 (the weakly linked candidate in the pair) was ON in either E6 or F1 it would force 8 to be in the other corners. We are looking for a diagonal Naked Pair - each cell can't see the other, but it is locked. If one of those candidates is linked to the other corners with strong links (ie no other n in the two rows and two columns of the rectangle), it could create a Deadly Rectangle. However, I am obliged to call Type 5 since I don't want to re-number everything.Īny rectangle across two boxes that contains two candidates in all four cells might have two opposite corners containing only two candidates, like the in E6 and F1. Since it is vaguely related to Type 1 (in that it attacks candidates in the rectangle, not outside), and is quite simple to spot, the solver searches for it after Type 1 and before the others. Not to say that it might have been discovered elsewhere, I can't check, but please come forward if there are earlier references. In the red example, swapping within the box does not change the content of that box.Īs of January 2021 we have a new Unique Rectangle elimination! Thanks to Ivar Ag�y from Norway who shared an example with me. Why? Swapping the 7 and 9 around places them in different boxes and 1 to 9 must exist in each box only once. One of them is the real solution, the other a mess. Now, such a situation is fine since you can't guarantee that swapping the 7 and 9 in an alternate manner will produce two valid Sudokus. The 7/9 still resides on two rows and two columns, but instead of two boxes it is spread over four boxes. The pattern ringed in green looks like a deadly pattern but there is a crucial difference. If you have achieved this state in your solution something has gone wrong. There are two solutions to any Sudoku with this deadly pattern. But it would be equally possible to have 5 in that cell and the others would be the reverse. If the cell solution was 4 then we quickly know what the other three cells are. Such a group of four pairs is impossible in a Sudoku with one solution. ![]() They reside on two rows, two columns and two boxes. ![]() The pattern in red marked A consists of four conjugate pairs of 4/5. In Figure 1 we have two example rectangles formed by four cells each. ![]()
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