Bug Reports

[SudokuMonster]

@1to9only reporting the bug:

This SukakuExplainer (private build, version 1.17.11) solves this X-Windoku incorrectly, and chokes up...

.......1.....2...3.........4....3.......5...6....1.........78......6........32... ED=20.0/9.4/2.9
23954671851792864368437125942568397197125438686371942535.19786279246513.146832597

1to9only's SukakuExplainer rating (private build, version 2021.6.17):

.......1.....2...3.........4....3.......5...6....1.........78......6........32... ED=9.6/9.4/2.6
932674518678521943541398267469283751217459386853716429326147895794865132185932674

X-Windoku from this m_b_metcalf's post: http://forum.enjoysudoku.com/post309317.html#p309317

@1to9only original comment on the bug: I've looked at SukakuExplainer' solution path, and it goes wrong at step 64:

4.3, Grouped 2 Strong links 101: Cell r9c7,r7c9,r7c5,r1c5 on value 4: r1c6<>4

It removes candidate 4 from r1c6, when it is the cell solution.

If you disable the 'Skyscraper, Kite, Turbot' solving technique, the X-Windoku solves OK, X-Windoku rating: ED=9.6/9.4/2.6. From the command line, specify: --techs=1111111111010111011011111011100111100111111111

Originally posted by @1to9only in https://github.com/SudokuMonster/SukakuExplainer/issues/111#issuecomment-917418603

Screenshot of Step:

SukakuExplainer 1.18.0 explaining the logic which was incorrectly applied Grouped 2 Strong links 101 This technique relies on Conjugate Pairs that infer a strong link and/or a special arrangement of values in a line or block also known as Grouped Strong Links (where a strong link is inferred from groups of cells having the same value). These use strong links in Location inferred from 1 value (L1), therefore, Grouped L1-Wing can be used to describe this pattern.(Currently, L1 is reserved for 3 strong links). the arrangement of cells with value 4 in block 9 and column 5 form strong links (conjugate pairs, shown as green values) or grouped strong links (orange cell outline or yellow cell background). These strong links are weakly linked to each other via window group 8 and window group 8 (Red or Green outlined region). Any occurrence of the value 4 can therefore be removed from any cells sharing a region or regions with ALL cells with value 4 in block 9 and column 5 that are not part of window group 8 or window group 8. This technique is part of more generalized technique called X- chains which in itself is part of more generalized technique called Alternating Inference Chains (AIC). This technique uses logic closely related to Finned X-Wing technique logic. The grouped strong link when inferred from cells in a block that are arranged in one mini-row and one mini-column is also known commonly as "Empty rectangle". The inference of a strong link from a group of cells with value 4 in any region can be spotted when a an "Empty mini Area (EmA)" is observed. This EmA could be an empty mini-Line (EmL) in a region or regions. In the case of "Empty rectangle" the EmA is a group of empty cells that can also be referred to as "Empty mini Rectangle (EmR)".