I don´t want to make you mad, I just want to clarify, that I asked you in your scenario: "May i use this scenario as a template for my seminar paper? :)" 2013/4/3 "Of course you can." And the text in this scenario is just a mention.

@Gevater_Tod4711 I HAVE asked you ;) Look in the comments of your scenario: http://www.greenfoot.org/scenarios/5853 And in the instructions of my scenario: "The design of the numbers, the playing board, the red selection square an the messages were made by Gevater_Tod4711 "

Thank you very much for you´re instant feedback! I am aware that this sudoku can have more than one solution and I´ll try to fix it. But it´s still solvable, you just can´t call it uniquely solvable. (http://en.wikipedia.org/wiki/Mathematics_of_Sudoku#Enumerating_Sudoku_solutions) However, I hope I can solve the problem.