Mathematician Claims Breakthrough in Sudoku Puzzle (Scientific American)
Basically, a mathematician used a rarely-used method for proving that 9×9 Sudoku puzzles with less than 17 clues are unsolvable. (That is, they have multiple possible outcomes. A 'clue' is an initially filled-in number on the Sudoku grid.)
I knew Lummox JR had some interest in Sudoku puzzle generation, so I thought perhaps this would interest him. (And others as well, of course.)
Sudoku puzzle generation and difficulty scoring are very complex issues.
Perhaps this discovery could make that problem a bit easier.