billablog

Here's a puzzle generated by Sudoku.Coach and posted by u/ddalbabo on Reddit. SC's "Beyond Hell" grids are always a treat, often on the very edge of requiring Forcing Chains. Discussion link Puzzle string: 010000800025060000780001904000300000050100009800000010000020540090800106003600000 Sudoku.Coach SE = 9.0 according to SukakuExplainer. YZF says 8.8. Not sure what's going on there After basics (7)r6c49 = (4)r6c4 - (4=9)r2c4 - r2c1 = r4c1 - r6c3 = (9)r6c5 => r6c5<>7 What immediately jumps out to me is this Bivalue Oddagon of {25}. We can build an AIC off the guardians and eliminate a 7. I couldn't find any other more useful chains using this so it's back to the drawing board for now. The next move uses a DoF>1 AIC so read  this article  if you haven't already. (4)r6c7 = [(4)r8c5 = r9c6 - r9c2 = r4c2 - (4=26)r46c7 - (2=7)r9c7 - (7=4)r9c2 - r9c6 = (4)r8c5] => r6c5<>4 You could call this a Kraken ALS? The 2 DoF component here is (4)r4...

  In this post I'll be tackling the weekly "Unsolvable" puzzle from  SudokuWiki . This week's puzzle was provided by Richard Kröger.  Puzzle string: 2....4.....8...3...9.1....74....2..9..3.......1..7..5..6.3..1.......8.2...7.5.... Sudoku.Coach SE: 9.0 Starting off with basics - click images to enlarge. Hidden Pair Swordfish Finned Swordfish XYZ-Wing ALS-AHS-XZ: (28)(r3c7 = r3c58) - (8=1695)r1c3789 => r3c7<>5 AIC: (5)r1c7 = (5-7)r8c7 = r8c4 - r1c4 = (7)r1c2 => r1c2<>5 Grouped AIC: (7)r7c8 = (7-5)r8c7 = (5-9)r1c7 = (9)r89c7 => r7c8<>9 Grouped AIC: (9=7)r7c6 - r7c8 = (7-9)r8c7 = (9)r9c78 => r9c46<>9 At this point classical AIC fail us so we need to use branched chains. Read  this article  if you're unfamiliar with the concept. [(3)r6c6 = r3c6 - r1c5 = (3-7)r1c2 = (7-1)r2c1 = r9c1 - (1=6)r9c6] = (1-3)r8c1 = [(3)r6c6 = r6c9 - r8c9 = r8c2 - r1c2 = r1c5 - r3c6 = (3)r6c6] => r6c6<>6 You'll see within the square...