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.
Systematic Sudoku 
Can you tell me what system are you utilizing on this web site?
Yes, Monika. I’m using WordPress, with ‘Twenty Ten’, probably the simplest theme. I describe production details in the Tools page. The media inserts are all pictures made from PowerPoint slides. The gray highlight texts are pictures of text boxes, mostly loaded from slide comments.
Hi.
Discovering your blog. Thousands thanks, I like the approach. I try myself to avoid filling grids with unnecessary candidates, and I like the systematic approach of marking lblocks and rows.
I do not understand why at r7c8 you get “1467” and not “12467”.
Thanks for the comment. I’d like to know if you do anything close to slink marking and the bypass.
The missing 2-candidate is an error. The real problem is deeper. Ardson’s 38 was miss copied and this error forced the bad copy to a solution. This situation is mentioned in the post introduction, and again in the post of 5/30/17. The solution path of the corrected Very Hard 38 is in 7/04/17, and some lessons learned about multiple solution puzzles and backtracking solvers in 7/11/17. I really should update the review to reflect improvements in Sysudoku since then. In Sudoku time, it was long ago.