Mathdoku
(Published in Czech Republic Academic Championship)
Write a single number from 1 to 9 in each cell such that each number appears exactly once in every row, column and bolded 3x3 box. For more, in each of nine nonets (3x3 squares) there are subsidiary numbers between two cells. These numbers are the results of binary operations (addition, subtraction, multiplication, or division) between the two cells. In each nonet there must be used all the four binary operations.
