A Box ALS in Left Page UHC 89

In this post, a large box ALS with many outside candidates becomes a starter in AIC building, and a second cluster becomes a AIC target. 

Restoring 2r8c7, we continue with an box ALS node AIC chain, using its 5 value group in an  ANL. It could be started as  that same 1-way with 8 targets of the previous post, and continuing to 2r9c3, when we notice the possibility of an ALS with 2 and 5 value groups for the grouped ANL. Instead of enumerating ALS, this is recognizing them as needed, certainly in the spirit of AIC building.

This could lead to another chain going back along the chain to another 5 seeing 5r6c2 and the resulting boxline.

After a small follow-up

I finally get a XY AIC offer from Beeby, making it a promising time to start a new coloring cluster.

The ANL produces a pair of 2’s guaranteed to include the true one, and completing a hidden dublex 2-wing.

The pair also remove 2r9c3, converting the SW five cell ALS into a naked quin.

A second XY ANL escapes the red/orange cluster to expand the blue/green cluster,

trapping 5r2c8 to expand red/orange to trap 9r89c9.

We also get a sweeping shortcut 3 – ANL.

Note that 3r1c9 seeing orange means that any red 3 in the cluster is a possible ANL partner terminal.

The AIC building party continues with a nice loop making very little use of the clusters. The removals are based on the fact that every link in a nice loop includes a true candidate.

Here is the 3-panel showing the 3 removals from the nice loop. The panel is marked in an unused row to show the finned swordfish in columns 2, 4 and 8. The fins are the 3s marked f. If the fins are removed, columns 2, 4, and 8 will share row positions 3, 6,  and 9 marked by + signs in an unused column, forming a swordfish. The swordfish removes candidates in other columns in its three rows.

If 3r9c1 is true, the fins are removed, the swordfish forms, and removes 3r9c1.

On the grid, the row swordfish icons show the column positions sweeping other columns. Small rounded squares mark the fin candidates, and the diamond marks the removal.

After a short follow up, it takes a few AIC and another finned swordfish to wrap ultrahardcore 89. You might like to do it ahead of the next post, which will show added possibilities of AIC building around a cluster.

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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