i remember doing something like this a long time ago with the easter monster puzzle, it must have been 2009-2010 because i do remember that whatever i wrote got lost in the big forum crash.
i don't remember how i came up with this exactly, but my solution idea was to systematically try out all possibilities of r4c8 and r8c4
here is the pm grid after the infamous sk loop and secondary eliminations
- Code: Select all
+----------------------+----------------------+----------------------+
| 1 478 3458 | 3567 389 5678 | 3489 369 2 |
| 238 9 378 | 4 126 1267 | 138 5 368 |
| 3458 248 6 | 1235 389 1258 | 7 139 3489 |
+----------------------+----------------------+----------------------+
| 2468 5 1478 | 9 126 3 | 128 1267A 678 |
| 3489 126 3489 | 126 7 4 | 3589 126 3589 |
| 2369 1267 1379 | 8 5 126 | 1239 4 3679 |
+----------------------+----------------------+----------------------+
| 7 148 4589 | 1235 348 12458 | 6 239 3459 |
| 456 3 145 | 1267B 126 9 | 245 8 457 |
| 4589 468 2 | 3567 348 45678 | 3459 379 1 |
+----------------------+----------------------+----------------------+
i have marked cells r4c8 and r8c4 with A and B. notice that the strong links on 7 in c8, r8 and b9 mean that either A or B must be 7, but not both. this gives us 6 possibilities
A,B =
1,7;
2,7;
6,7;
7,1;
7,2;
7,6out of these 6 possibilities,
3 of these resolve to a contradiction using basics and turbot fish,
1 gives a contradiction using basics plus turbot fish and an xy-wing, while the other
2 give a contradiction - or
solution - using no more than basics and one or two wing patterns (combos of 3 strong and 3-4 weak links with their own names). nothing more is needed, and the end result is what i think is a pretty nice solution to the easter monster with just a simple case breakdown and no chains at all
edit: to answer the op's question, this is equivalent to saying that 2r8c4 solves the puzzle by itself with the sk loop and a couple of wings, which while not a one-step solution is still quite nice. however, this approach also considers what happens if you don't assume 2r8c4 as well