Author Archives: Sudent

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.

Wrapping Up UHC 89


This post completes a coloring solution of Stefan Heine’s left page ultrahardcore 89.  Two examples of cluster exit AIC building bring a second finned swordfish, and a cluster exit wrap of the large cluster. After this follow up of last … Continue reading

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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 … Continue reading

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UHC 89 Breaks Out from a Monster Basic


This post coordinates the two DIY solvers used in the ultrahardcore review, choosing and interpreting solver methods and ignoring some removals to match the Sysudoku DIY order of battle. A series of early moves breaks the ice for AIC building … Continue reading

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A UHC 45 Discontinuous Nice Loop Seminar


Heine’s left page ultrahardcore 45 offers a host of examples illustrating when a Beeby “discontinuous nice loop” is and isn’t a 1-way. Coloring closes the class. UHC 45 has a remarkable number of bv and line slinks, given the monster-like … Continue reading

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Pattern Analysis with Coloring on UHC 1


Coloring can be combined with freeform pattern analysis to determine a small set of pattern trials for Heine’s ultrahardcore 1. Typical choices for this decision are reviewed. A single trial produces the solution. For this we go back to the … Continue reading

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Single Alternate SdC on ultrahardcore 1


This post reports a rare outcome in an SASdC trial, the extra term carrying through to a solution. Here is the grid with NWc1 marked as a Single Alternate Sue de Coq chute. The contents of the wall can be … Continue reading

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Heine’s ultrahardcore 1 Starts the Review of Left Pages


This post whittles on a tough grid, duplicating results of the two solvers by different means. When the solvers stall, we find a Single Alternate Sue de Coq for readers to try. Sysudoku Basic brings four clues and  slinks, but … Continue reading

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Coloring KDST 5 10 5 is Too Easy


The bypass almost finishes KrazyDad Super-Tough v.5, b.10, #5, whether or not you start with the 4-fill and two 3-fills. Here’s my 4-fill version. Line marking is minimal, and coloring on the few candidates remaining wraps green in r6. With … Continue reading

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A KDST 595 Hidden Weakness


In KrazyDad SuperTough v.5, b.9, n.5, an almost naked triple is concealed, awaiting a single elimination. It’s not something reasonable to search for, but two systematic constructions get you there. An otherwise anemic bypass fills the NorthEast box, but slink … Continue reading

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KDST 585 Favors the Bypass and Coloring


In spite of a big bypass, Krazydad Super-Tough v.5, b.8, #5 requires some work. An extensive XY railroad looks good, but a comparison with Medusa coloring favors the latter. This brings an opportunity to show unusual coloring resolutions, one involving … Continue reading

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