Here I report on 4 and 24, the first two of 10 puzzles selected for the Sysudoku review of the FTSPAH puzzle book. Starting grids were displayed at the end of last week’s post. I also explain a few things about the blog to a high school classmate, Jimmy.
FTSPAH has no acknowledged author, publisher, or copyright notice. The full title is spelled out in the previous post, and that’s quite enough. We are told it comes from Middletown Delaware, and that its “200 DIFFICULT puzzles … have the ability to cause even the most seasoned Sudoku lover to curse out loud in frustration”. Sysudoku readers are not expected to be all that seasoned. A Sysudoku review shows what can be expected by a human solver following the Sysudoku plan of attack. FTSPAH is revealed to be not that frustrating.
Here is the bypass trace for FTSPAH 4. The given 2-fill and 3-fill have so many effects, the puzzle is essentially solved before the 1-9 values list begins.
Jimmy, traces allow readers to reconstruct the solution one move at a time. The reader provides the reason for each move. That makes it simple and informative. Experienced readers can write their own traces and compare notes. For help, see Sysudoku Traces on the menu bar.
Sysudoku Basic on Ftspah 24 is more normal. The challenge here is patient focus on your knitting.
The first advanced stop is the BV map, where the XY railway produces a simple XY ANL.
Jimmy, there’s a glossary on the menu bar. It’s Sysudoku Speak.
Basic is the collection of candidates. Advanced is using relationships of candidates and clues to remove false candidates and confirm true ones. All basic procedures and advanced methods are explained in a hierarchy of pages, The Guide. For a listing of post titles, go to Titles.
Then an XY extension of the XY chain winds through the bv field to produce a very long nice loop. Every pair along the loop is toxic. Every link of the chain includes a true candidate, a placement in the solution.
By Sudoku rules, two placements of the same value cannot be in the same box or line. So any candidate in a box or line with both link candidates of the same value is removed.
The strong link network reveals itself in X-chains and coloring. Here we get a 2-chain ANL. In an ANL, an Almost Nice Loop, at least one terminal is true. If you see both, you’re out.
Coloring reveals a lot more of the slink network. Traps at r3c3 and r7c3 expand the cluster to force a wrap of green in r1c5. The blue army mops up.
One color is true, therefore seeing both colors of the same value is fatal. Two candidates of the same color in a cell is fatal for that color. That’s one type of wrap.
Here, the trap of 9r7c3 colors 9r7c1, and that traps 3r7c1, because blue or green is true.
Jimmy, I don’t usually repeat the fundamentals, but in this post it’s to show you around the place.
Next week we pair FTSPAH 44 at left with 84 on the right. One is basic level, the other, advanced. Find out which before the post comes out.