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.

UHC 177 Introduces a Beeby Option


This post gets left page ultrahardcore 177 to coloring with an interesting Sysudoku Basic and a kraken X-wing accessed with a recently added AIC option. Stefan Heine’s ultrahardcore 177 makes many left page concessions, but makes a fight of it. … Continue reading

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Closing Out ultrahardcore 133


Resuming on ultrahardcore 133 after two 1-ways, and a r1 naked pair 16 removing 16r1c3, and the resulting NW naked pair 48 removing 4r3c3.  Solver Beeby finds this ALS node AIC. Starting from 6r2c9, it was a possible exit from … Continue reading

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Ultra 133 “Simple” Chains and Discontinuous Loops


After an productive naked triple in line marking, and two bv scan methods, left page ultrahardcore 133 starts AIC building with Beeby “simple” chains. Then we take in two “discontinuous loops, i.e. simple 1-ways. The decisive ALS AIC’s and colorful … Continue reading

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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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