An ultrahardcore 221 ALS AIC Clinic


Continuing a solution path with a finned starfish (5 lines), Beeby carries us through an unlikely  series of ALS aided AIC, dancing around two stalled coloring clusters. The contest ends with regular AIC finally expanding and wrapping the clusters.

Here is the finned starfish, with a coloring “observation” as a possible start.  It went nowhere.

The starfish on columns occurs if fin 6r3c4 is removed. It’s victim, 6r1c5 sees the fin. So if the victim is true, it removes the fin, and is eaten by the starfish.

The starfish has victims r125c1 as well, but if any one of these is true, that would confirm the fin and prevent the starfish.

A second cluster has a better start.

The next Beeby find, an unlikely looking ALS chain , starts as a 1-way from 7r7c2. To spot this ANL, however, you need to have an ALS map with 6r9c3 identified as an ALS single.

Next is a second ALS chain grouped ANL which first uses a bv a7c2without regard for the ALS, then takes a  shortcut through the red/orange cluster to enter the ALS at 1r4c2, using its 6 value set as an ANL terminal group.

Again, you have to recognize ALS c2 1457/13467 to spot this possibility.

Going for a third strike? It won’t win the game, but on this shot at the 7’s seen by 7r1c5, we must have tried every other red candidate before 8r5c1, then seen the route to the c7 ALS with single 6 and 7 value set.

Having run through the available ALS node AIC, Beeby responds to a request for simple ALS with this ALS_62. 

I remembered the SW ALS from the ALS_26 I recognized as duplicating the Sudokuwiki APE. Both of the ALS here have been available since 6r3c9 was removed by the complex chain just before the finned starfish.  

However, the removal expands the blue green cluster to reach another ALS single with a 7 value set. What’s missing from this report is the three part ALS map you and I would need to ever spot this. Beeby reconstructs it on the fly every time we ask for an ALS AIC.

Running this option dry, I ask for an ALS wing, which is a chain of ALS, including bv.

This one combines a boxALS and a row ALS, tied together with a bv. One uses a value set for an AIC starting slink, the bv does its normal node job, and the third uses its value set as a pointing group for an ANL.

The removal leaves a clue and a naked triple in r1.

Now two more simple chains. First, a new 1-way turned ANL, which enables

a second, decisive ANL. As traced below, it expands both clusters,

trapping 7r7c6 to wrap orange.

Then, after the red confirmation   follow up,

a 7-chain finishes UHC 221.

Next week we start left page ultrahardcore 265. 

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.
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