The one thing that's not mentioned in the article or the comments was that Jeffries had never played sudoku before this problem whereas Norvig presumably has.

The one thing that's not mentioned in the article or the comments was that Jeffries had never played sudoku before this problem whereas Norvig presumably has. It was after a few months of playing the game when I started thinking "Oh, this is just a constraint propagation search problem" and, indeed, when I had to code a solution for a programming competition, it took about 45 minutes to hack together the code.