Hi out there, What i like to know, is how could you know, that a sudoku-like number table is a real sudoku with only ONE SINGLE solution? The Solvers from the quiz (which I did not read) will surely find a solution. But where did the sudokus themselves came from? What about a sudoku-generator? Which leads to: How to proof a certain number table has one and only one solution? Maybe the solvers do that already? And if so, which one does? Sorry for the memo-style onf the message. It just came to my mind and had to be written down. regards ralf -- > "not using Ruby is punishment enough" > -- James Britt, 8.5.2005, ruby-talk / ruby-lang.org