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.

Beeby on Heine’s ultrahardcore 3


This post highlights several moves from Phillip Beeby’s solver, which are alternatives to those appearing in the five earlier posts on Stefan Heine’s ultrahardcore 3. One result is a solution without the second blue green trial, left as a project … Continue reading

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Readers Solve Ultrahardcore 3


This post returns to the Stefan Heine’s utrahardcore  3 solution path just before cell and unit forcing chains. It turns out that an immediate coloring trial reaches a solution without them. Then we report how two Sysudoku readers solve it … Continue reading

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Ultrahardcore 3 Falls to Coloring Trials


This post reports coloring trials that gain the solution after forcing chains when Sudokuwiki gives up.   This includes an example of a grid diagram illustrating the route to contradiction in a breath first trial trace. Then we close with a comment  … Continue reading

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Ultrahardcore 3 Schlagt Forcing Chains


In this post, we continue with Sudokuwiki into forcing chain methods, and their relevance to the ultrahardcore theme. Sudokuwiki stalls, as Stefan predicts.  Then we fashion a trial for a logical, but practical outcome. On the grid after the red/orange … Continue reading

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Cell and Unit Forcing Begins in Ultrahardcore 3


This post reveals yet another way to start a boomerang, and reconsiders the practicality of Andrew Stuart’s Cell  and Unit Forcing Chains, this time facing an ultrahardcore right page. We get to a choice between Sudokuwiki and a coloring trial … Continue reading

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Utrahardcore 3 Lifts Off


The review of Sudoku ultrahardcore 1 right pages, a separate collection from (and tougher than) its left pages, begins with number 3, shown here post before last.  In this post, we follow Sudoku Basic and the Andrew Stuart’s Sudokuwiki solver … Continue reading

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A Bracket Busting Dave Green 4-Star


Here’s the  basic trace on the Saturday Dave Green 4-star shown at the end of last week’s post. It survived the three Sysudoku Basic  phases: bypass, box marking and line marking. It’s the first I remember. Let’s talk through the … Continue reading

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Puzzleproof’s Sudoku Extreme Is Good Basic


Finishing with no advanced moves, the Extreme Sudoku 2 collection proves less than extreme. However, the collection, including the last three selected puzzles, 154, 175 and 196, have many worthwhile examples of basic slink marking in action. In the Pzlpfx2 … Continue reading

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Double Sweep Lessons From 112 and 133


Two rare double sweeps in the bypass show up this post. In Puzzleproof Extreme 122, it’s a 5-fill line; in 133, a 5-fill box. In each, 5 cells are free and two are claimed by two values, leaving a 3-fill. … Continue reading

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Can Box Marking Be Extreme?


This post continues the Sysudoku Basic review of Puzzleproof Extreme Sudoku 2, with reports on 70 and 91. In the basic trace of Pzlpf2 70, there is the typical heavy bypass, and collapse in the 9: box marking list. The … Continue reading

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