billablog

Read Part 1: Introduction to AIC     This is part 2 of my article on AIC. Originally it was part of the original article but it got so long that I felt it was detracting from the focus of the original, so I decided to split the article into 2. Please read part 1 if you're unfamiliar with the concept of AIC.

There is no Sudoku technique which has been as frequently mistreated and misunderstood as Alternating Inference Chains. Since  its introduction in 2006  it has become the most popular chaining method, but despite that, there are very few resources online that correctly detail the concept as originally expressed. Instead the majority repackage an earlier chaining technique called Nice Loops, changing a few terms here and there.     

Alternate title: solving the most epic extreme hardest most difficultest puzzle ever made

In this post I'll be solving the puzzle Loki, published by mith in 2022.  Here's a link to the original thread. Loki broke many records and was dubbed the "hardest puzzle in the world". It is one of the few puzzles with SE 11.9, if I recall correctly the 10th to be found. 11.9 is conjectured to be the maximum possible difficulty in a Sudoku puzzle. It was also the first ever puzzle proven to be in T&E(3), breaking a decades-old conjecture that 2 was the maximum. Its discovery opened the floodgates and since then the users on the Sudoku Players' Forum have been largely dedicated to exploring its offshoots and generating hundreds of thousands of extremely difficult puzzles utilising 3-digit chromatic impossible patterns. But can a lowly human solve it? Let's see.  

In this post I'll be tackling the weekly "Unsolvable" puzzle from  SudokuWiki . This week's puzzle was provided by Andrew Stuart. 

   In this post I'll be tackling the weekly "Unsolvable" puzzle from  SudokuWiki . This week's puzzle was provided by Andrew Stuart. 

  In this post I'll be tackling the weekly "Unsolvable" puzzle from  SudokuWiki . This week's puzzle was provided by Andrew Stuart. 

In this post I'll be tackling the weekly "Unsolvable" puzzle from  SudokuWiki . This week's puzzle was provided by Andrew Stuart. 

u/Ok_Application5897 posted this puzzle on the Reddit today:

 Someone on the r/Sudoku Reddit posted this puzzle innocently asking for help:

   In this post I'll be tackling the weekly "Unsolvable" puzzle from  SudokuWiki . This week's puzzle was provided by Andrew Stuart. 

  In this post I'll be tackling the weekly "Unsolvable" puzzle from  SudokuWiki . This week's puzzle was provided by Richard Kröger. 

In this post I'll be tackling the weekly "Unsolvable" puzzle from  SudokuWiki . This week's puzzle was provided by Richard Kröger. 

In this post I will showcase a rather interesting interaction between two AALS that share a cell. This came up within an SE 8.3 puzzle I was solving and delighted me with its simplicity and its practicality (it immediately reduced the puzzle to basics). It is very similar to Sue de Coq. I'm sure it's known but I've never seen it brought up before. Typically when chaining off AALS, the easiest option tends to be to use region-wise interactions with ALS weakly linking 2 candidates at once. 

 In this post I'll be tackling the weekly "Unsolvable" puzzle from  SudokuWiki . This week's puzzle was provided by Richard Kröger, as with last week's. 

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.

  In this post I'll be tackling the weekly "Unsolvable" puzzle from  SudokuWiki . This week's puzzle was provided by Richard Kröger. 

I've been learning advanced Sudoku tactics for about 2 years now and lately I've been venturing into the world of branched AIC. It's very work-intensive to identify useful examples, but the results are equally rewarding.  2025-11-27 update: I've disowned this article in favour of  Almost-AIC as outlined in my AIC article . This article's conception of branching AIC was quite silly and admittedly motivated more by how pretty the graphs could be than by practicality.