Pattern Coloring Not-Both on Only Extreme 261

On this post of the Manuel Castillo Only Extreme review, Only Extreme 261 justifies its “extreme” label. After limited advanced moves, a pattern based coloring suggests an extension via a not-both trial on a long AIC strong link. The not-both trial rejects the coloring by reaching the solution. A counter trial assures that this unexpected result does not signal a multiple solution. In the  update post of 4/30/19,  trials are avoided as the same coloring is extended.  

First, the basic trace. Simple to follow, but leaving a distracting host of candidates, and not many clues, on the grid.



My first advanced nibble is a 7-chain and extended chain (red) for two almost nice removals in c8.









One of them enables an irregular 562 wing. The weak link attaching the 26 wing is a 6-chain, lining 2’s up for the victim.


It was a bad day for fishing on the X-panel, but 7-freeforms from the West side were only three.  By assigning colors by starting point, and coloring only where all patterns of a color cross, a blue/green cluster is created. Only the blue or the green candidates in common, can be true.



Applying this coloring to the AIC grid, where several AIC  chains had been fruitless, the conflict between the blue and solid green patterns at r4c7 could be resolved by a not-both extension. In this case it has the same result as a color trial.  With little else to go on, a color trial on this small cluster is in order.




Before the trial, however, there’s a cheap removal to take.  In a red/orange coloring  of 8-freeforms from West to East, the ending candidate on the same row will have different colors. We don’t have to enumerate the freeforms for the trap.



In the trial, if both 7r9c4 and 7r4c7 are true, green is confirmed. The red/orange cluster explodes. There is no color wrap, but red forces two 5’s in column 5. Orange gives an immediate solution of Only Extreme 261.





This unexpected success leaves us needing to see if the AIC slink coloring, making 7r4c7 blue, brings more solutions. From the freeforms 7-panel above, the blue 7-pattern is confirmed in that case, and both green patterns are false. A trial trace makes it easy to demonstrate that no more solutions exist.  Blue implies red (E6) and forces two 2’s in c6. Time to move on to Only Extreme 304.



About Sudent

I'm John Welch, a retired engineering professor, father of 3 wonderful daughters and granddad to 7 fabulous grandchildren. Sudoku analysis and illustration is a great hobby and a healthy mental challenge.
This entry was posted in Extreme Solving, Puzzle Reviews and tagged , , , , , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s