A Run Through Ardson’s Very Hard Volume 2


This post begins a review of A.D. Ardson’s Sudoku Very Hard Puzzles, volume 2. The review will cover 10 pre-selected puzzles from 400, every 40 starting with number 38. Well, almost. The puzzle at the end of the previous post was number 38, missing a clue. We’ll go forward with this one, but will follow up with the real number 38 at the end of the review. The review table will follow in the concluding post.

Ardson’s puzzles start deceptively, with an generous set of givens, often with numbers completed through banks and towers.  For one thing, I’ve never seen the bypass start this way. Basic solving is usually balanced between bypass, box and line marking.  In the first review puzzle, Ardv2 38,  basic trace is typical, ending with a 9-wing.

After the removals, the  remaining 9’s form a dead swordfish (no victims). Did you try the UR opportunity, the 56r16c89 rectangle?

 

 

 

 

 

It’s a Type 4. One slink partner among the extras is true, so the other UR partner must be absent, else a deadly rectangle is guaranteed.

After a fruitless bv scan and X-panels produced only an anemic 9 – cluster, I put in AIC hinges, and extended the cluster via forcing chains. The chain 9r9c1 to 4r9c2 is an AIC slink! The next slink coloring 4r7c2 green traps 12r7c2.  Likewise the AIC slink 9r7c4 to 2r8c5 traps 67r9c5.

After these removals, 2r9c2 is trapped, because it sees blue and green. Another way to look at it, is that both blue and green erase 2r9c2.

It now becomes evident that green forces two 4’s into r9. Blue collapses Ardson v2 38 quickly.

An eventful basic, a classic UR, and SOB alternative but an unusual move to extend a desperate little cluster. Then a tricky trap for the extension that surrenders the green army. Not a bad start for the review.

OK, I’ll preview two more, giving you time to get your copy of A. D. Ardson’s Sudoku Very Hard v. 2 to stay ahead of me through the review. It’s number 78 for next week and 118 the week after. If you do ‘em differently, but logically, comment on the reporting post. But don’t tell me anything ahead of time. Let me suffer.

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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.
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