Only Extreme 218 Straight Up

Barely escaping the bypass, Manuel Castillo’s Only Extreme 218 gets tough, and brings out some seldom used methods. An alternative trial path by Single Alternative Sue de Coq, normally held in reserve,  follows in a second post.

The bypass filled in the center band and tower, leaving very little action for box or line marking stages.


Then 218 announced its intentions with irregular 457-wings.  First, consider the SE 57 wing winked to the NE hinge by a lumped 5-chain. Two regularly attached 47 wings pair with it to generate removals. In black, a lumped 5-chain hitches a ride on one link of the irregular 457 wink. One ANL victim requires 5-chain vision to see one of the toxic terminals. The SW 5’s provide a slink (orange) for the chain and a wink  (green)for the victim.

I don’t look for these things. They happen. We use slinks for chain winks all the time, but it’s rare to see two candidates slink and wink at for different removals simultaneously.

It was a glorious, but very short story. Nothing else on the bv scan or panels.  Adding some coloring and AIC hinges, I stumble on an ALS-XZ. The AIC builds itself into a nice loop, extending the red/orange cluster around the loop.  The loop then extends, through r7c2, carrying red/orange into blue green.




Looking for a bridge wrap,

not(green and red)

implies blue or orange. A candidate seeing both colors is out.

No takers on that, but an important  fact is illustrated. Coloring extends with AIC extensions of nice loop colorings, in this instance merging blue and red, green and orange.

In the first step, if 5r7c2 is true, red 5r7c7 is false, green 4 is true and blue2r8c7 is false, proving not-both and extending red/orange over blue green.

There is also  a 7-chain ANL.

As the AIC scaffolding is hauled away to the dump, 218 breaks down with an orange wrap in r7. Manuel’s solution emerges. What a nice advanced ride!

Next week, , a reminder of what to do when you’re stuck, as I expected to be here. We’ll do a deferred trial introduced in Sysudoku, the Single Alternate Sue de Coq, on 218.

Its on the line marked grid. Can you find it and run the trial?






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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