After putting up a decent fight in basic, Weekly Extreme 430 joins an embarrassingly long line of Weekly Extreme Competition puzzles defeated by the single alternate Sue de Coq, one my early advanced solving discoveries. This time it’s the verification of the second SdC that marks all the way to a solution.
On row 8, on the last row of 5 free cells, no 6’s were found outside of the South box, bringing a boxline removal.
NEr1 = 5(3+7)(1+9) will remove 7r1c3, if (3+7) is not missing.
But if (3+7) is missing, the naked pair 19 in the NE box requires a 1 or 9 from r1c3, removing the same 7r1c3. So it has to go, (3+7) is missing or not. We are led to look to see if the classic Sue de Coq created by the removal, removes anything else. But it does not, because the required ALS are not present in either remainder.
My next encounter is another single alternate SdC,
Wc2 = 2(7+8)(3+9)+923 ,
the extra term occurring when (7+8) is missing.
I had to work hard on the verification, but I can’t complain. Turns out, it was the solution.
The trace was folded at (C6, C1), to get it on the screen.
But next week, we take a short break on the Weekly Extreme review, to return to Antoine Alary’s “most difficult” of the 200 “toughest Sudoku puzzles known to man”. The reason is to help report an alternative solution by a Sysudoku reader, who took up the challenge and independently solved More Extreme 200 using his own order of battle. His comment appears in the More Extreme 200 post
You too can use comments on the Sysudoku blog to bring out alternative solving ideas. It doesn’t have to be a current post. You don’t have to saddle yourself with the management of a blog to do it. If you like, I’ll gladly add highlight grids and traces, while giving full credit to your contribution, in a follow up post similar to the one you’ll see next week.