Chaining Strategies are fundamental to solving tougher strategies and here I introduce chains and how to build them
The original 'world's toughest Sudoku' and a short explanation of why this solver still can't solve the puzzle
Possibly the latest 'untimate puzzle', created by Arto Inkala. This sparked some ideas about measuring the extremely difficult puzzles.
Some raw data on how often each strategies is used
I introduce a paper by Kevin Gromley, talking about a set thoery approach to Sudoku Strategies. March 2014
My response to Crooks Algoritm pointing out that is doesn't explain anything at all.