Dragging in Only Extreme 304

This post continues with three more trials, two to reach a solution, and one to guard against multiple solutions, in Castillo’s Only Extreme 304. This is getting reeeaallly extreme.

Last week, we managed to extend and XY-chain across the grid and over a the bv field of a coloring cluster, and by three not-both trials, extended coloring over this chain. The cluster expansion trapped a 7-candidate, but little progress had been made against the brambles above and below the cluster.

The last not-both trial was close to a blue trial on the completed coloring of the XY chain, so between blue and green, I choose blue for a coloring trial. As before, an 3-chain covers one 8 in c6, and 4r2c7 is confirmed to help confirm 8r7c7 to eliminate the other 8 in c6. Blue goes down.

When green bogs down,  another trial possibility emerges.There is a Single Alternate Sue de Coq:

SEr7 = 3(1+8)(4+9) + 934.

One chute cell is (1+8) or that alternative is missing from the chute.   In the latter case, the solution is exactly 934.

It’s not too surprising that (SE9, SE4)  marks immediately into the solution.  



The difficulties to this point argue for a final trial to guard against a multiple solution.  

We should see if the alternative chute description

SEr7 = 3(1+ 8)(4+9)

leads to other solutions.  The  good news is that the resulting clue 7r7c6 forces 1’s in r7c2 and r8c4, allowing no 1 in r9. Knowing this is impossible without a trial trace.

Next week, it’s on to Only Extreme 347.


About Sudent

My real name is John Welch. I'm a happily married, retired professor (computer engineering), timeshare traveling, marathon running father of 3 wonderful daughters and granddad to 7 fabulous grandchildren. The blog is about Sudoku solving. It covers how to start, basic solving to find candidates efficiently, and advanced solving methods in an efficient order of battle. It is about human solving methods, not computer solving.
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