Author Archives: Sudent

About Sudent

My real name is John Welch. I'm a happily married, retired professor (computer engineering), timeshare traveling, marathon running father of 3 wonderful daughters and granddad to 7 fabulous grandchildren. The blog is about Sudoku solving. It covers how to start, basic solving to find candidates efficiently, and advanced solving methods in an efficient order of battle. It is about human solving methods, not computer solving.

Bookends of the Only Hard


This post checkpoints the only sysudokie bypass casualty and the only sysudokie basic survivor, in this second review of Manuel Castillo’s Only Hard Sudoku collection. The report of my first review was posted 1 ½ years ago, March 29, 2016. … Continue reading

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A Well Hidden Pair in Only Hard 128


This begins a brief review of Manuel Castillo’s Only Hard Sudoku, preliminary to reviewing his more recent Only Extreme Sudoku. Both books are wordless collections of 400 puzzles, with identical formats. Thanks go to officers, members and guests of the … Continue reading

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AIC Slinks Finish Only Extreme 3


This post continues the finishing coloring cluster expansion in Castillo’s Only Extreme 3, via not-both testing of AIC slinks.  After extending the blue/green cluster in the North bank via AIC slink, we continue with a second AIC slink adjoining the … Continue reading

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Cluster Extension by Not-Both Trials


In this post and the next, the first puzzle of the Manuel Castillo Only Extreme Sudoku review, Only Extreme 3,  is taken ahead of the review of his Only Hard Sudoku. The reason is in the title. Rounding out the … Continue reading

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Badger’s Advanced Sudoku


This post highlights David Badger’s two advance puzzles in the Sudoku 1001 Hard Puzzles sysudokie review, both starting with the almost nice loops to be found along the XY railway. In 301, the black XY ANL removes two 7’s, and … Continue reading

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David Badger’s 1001 Hard Sudoki


David Badger, a prolific composer of giant grid Sudoku puzzles, now has a giant book of 1001 standard size puzzles, self rated as “hard”. The publication date, listed in the back,  is June 17, 2017. Here is the standard Sysudoku … Continue reading

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A Bifurcated Coloring of the AIC Slink


In this post, the AIC slink produces an alternative solution of a puzzle originally solved by a rather extreme pattern coloring analysis. This solution demonstrates how the AIC Slink enhances the already powerful technique of Medusa coloring. The July 11 … Continue reading

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