I'm sure this issue's been raised before, but I think it's interesting. How can someone claim copyright on an individual sudoku puzzle? You can think of a sudoku puzzle as a mathematical object, so it's similar to me claiming copyright on the quadratic equation x^2+3x-4 or even the equation 3x=12. You think that sounds daft?

OK how about a system of 81 simultaneous equations in 81 unknowns? Now it's something similar to a sudoku puzzle. Also I'd have to put in a lot of work to ensure it has a valid solution and indeed a unique solution. Then if you think I can copyright that then why not a system of 12 equations in 12 unknowns? or 2 equations in 2 unknowns? or indeed 3x=12?

I'll play devil's advocate. One argument in favour of copyrighting a puzzle would be that given the number of possible sudoku puzzles, I'd have more chance of winning the lottery two weeks in a row than independently creating a sudoku puzzle identical to one already in the public domain. Well given the time of year, many people might try creating a heart shaped sudoku. Now if people are trying to create a puzzle with the clues distributed in the same fashion, then suddenly the chances of creating identical (or structurally similar) suddenly become much greater. A search on google images for heart sudoku only comes up with one image (somewhat surprisingly). When I first tried to create a heart shaped sudoku, I chose an almost identical distribution of clues, although I was unaware of that puzzle. However one flaw with this argument is that the two heart shaped sudoku I have created have a different distribution of clues (and slightly different from each other too). Also one other heart shaped sudoku referred to on a thread in rec.puzzles is different again. Nevertheless certain arrangements of clues are more aesthetically pleasing than others, so the chances of recreating a copyrighted puzzle must come down.

I must say as a disclaimer that I haven't made any money from any sudoku I have created (athough I wouldn't pass up the chance). Also I've not tried to create a sudoku with clues distributed in the same way as a published sudoku and tried to pass it off as my own. (Trying to find puzzles with the same distribution of clues is an interesting exercise though, especially when it leads to puzzles with different difficulty ratings).