# Tag Archives: XY-chain

## Mike Peterson’s Very Hard Sudoku, v.1

Resuming posts after a quiet summer, this review identifies the title book as a basic level collection, offering an interesting challenge for the slink marking bypass, and little else.  The brief  introduction offers interesting historical facts, but is another example … Continue reading

## Cycling Blindfolded with the Guide

This post calls out Gordon Guide misguidance related to coloring, slink chains and the XY chain. AIC fundamentals are omitted in favor of ineffectual strategy and renaming of well known AIC formations. First, lets checkpoint the basic solving of the … Continue reading

## Wings and Chains With the Gordon Guide

This post reviews the Chapter 9 of Peter Gordon’s Sudoku Guide, entitled Forcing Chains and Grid Coloring. The guidance is very limited, and what there is, promotes guessing as opposed to solving by logic. This verdict is confirmed in the … Continue reading

## Bent Naked What?

Here I object to Bob Hanson’s use of the XY-wing and the XYZ-wing, in Sudoku Assistant – Solving Techniques, to introduce his more complicated concept of “bent naked subsets”. This treatment limits the wings to unit based links.  Also I’m … Continue reading

## Shortz’ Ferocious Falls Short

Here I have to report a surprisingly poor showing, as an advanced solving collection, of Will Shortz’ “Beware! Very Challenging” puzzles from his 2008 book, Ferocious Sudoku. Will Shortz collection books are by far the best known among U.S. Sudoku … Continue reading

Posted in Advanced Solving, Puzzle Reviews, Shortz | | 2 Comments

## Stephens Extremes Snapshots I

Here we have highlight snapshots from the review puzzles from Paul Stephens’ Extreme collection.  Recent posts have been about the Stephens approach to basic and advanced solving.  The Sysudoku solving of two of the review puzzles, Weeks 48 and Addicts … Continue reading

## Absolutely Nasty 4 Review Snaps I

Here we link back to advanced solving posts as we enjoy sysudokie solving snapshots from the review table puzzles 0f Frank Longo’s Absoutely Nasty Level 4 (AN4) collection.  Did you ever get trapped looking at a neighbor’s vacation slides ?  You … Continue reading

## Toxic ALS in Unsolvable 40

Our struggle with Unsolvable 40 continues with a detailed walk through of the search for ALS toxic sets, and an analysis of the its stuck number ALS. Here is our grid with row ALS superimposed on a thin, as yet … Continue reading

Posted in Advanced Solving | | 1 Comment

## Alternate Inference Chains (AIC)

Readers of this blog are familiar with an alternate inference chain in the form of an XY-chain on a bv map, or an xyt-chain on the grid, or as an X-chain or grouped X-chain on an X-panel.  Humans, as opposed … Continue reading

Posted in Advanced Solving | Tagged , , , | 2 Comments

## XY-Loops

Denis Berthier in his Hidden Logic of Sudoku,  makes the statement that XY-loops are worthless.  Since we had such productive fun drawing curves through the bv cells – including XY-loops – back in the posts of December 2011, I should explain why sysudoku … Continue reading