An Error Hides a Lite Coloring Trap on ultrahardcore 399

This post corrects an error on the post of December 8, that prevents a lite coloring trap in ultrahardcore 399. Then there’s follow up on the trap, with the lite coloring marking in place. Trial is not avoided, but the lite coloring hastens the final wrap by contradiction.

Here’s the correction on a  goof by yours truly. On the APE by Sudokuwiki  and ALS_87 by Beeby, I deleted 7r3c8, instead of 7r2c8. In the post, that error is carried forward without incident, not affecting any eliminations or the coloring trial which solves 399.

Now coloring lite has a trap, on that very 7r3c8 spared by my error.

7r3c1 is blue lite, 7r6c8 is green lite.

Reader Dov Mittelman spotted a second lite trap, at 3r3c1, seeing blue lite 7 in r3c1 and green lite 3r6c1.

Beeby was enlisted, by stepping through its former finds and using its REMOVE feature, to take out the lite traps.

The 3r3c1 removal enables a finned swordfish, before the boomer from 7r6c8.

Also, a complex 1-way from 7r3c1, which sees the victim and starts the branch hacked slink chain to the other terminal of the ANL. True or not, it wipes out 7r3c5 and becomes the winning 7-candidate on r3.

After NW7, Beeby runs out of even the unlikely human options.

There are alternatives to the green coloring trial of the review. The green trial comes with the green lite trees. But the other options are advanced by the lite coloring.

Cc4 contains 6(1+8)(4+5), so orange comes with a C45 pair.

The SASdC in Nr1 ,

Nr1 = 5(3+9)(2+5) + 572 comes with the aqua candidates

Also there’s a pattern situation on the 7-panel left by my  r3c8 lite removal.

The short dashed pattern reaching r1c2 is rejected by Dov’s lite trap, leaving  the third tan/aqua cluster in the 7’s to be decided.

The point is that lite coloring enhances trials, when it fails to avoid them.

This time, compared to the green trial in the review, the green clues change little, because we have already incorporated most of their effects. The color expansion is in the red/orange cluster, which grows in a distinctive way, by adding naked pairs.

looks like I may have to try the red or orange army. Then I notice that in r2, orange will enable a now naked triple to confirm 4r2c5 and then red 1r2c1. No, Virginia, orange doesn’t get to confirm red. It gets tossed for trying, and collapse follows.

Compared to the review post, the color solution has the same reds, but a few more greens.

There’s now a lite coloring page in The Guide, mostly based on last week’s post. It’s a child of the coloring page (drag off right). Guide pages on Sysudoku trials are coming soon.

As to posts, the next one will look back to a previous attempt to extend coloring. Suggestions on collections to review or topics to explore are welcome, either in comments on posts or at Please attach comments to relevant posts.

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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