Antidiagonal Twin Detector Sudoku
(Published in Czech Republic Championship)
Place a digit from 1 to 9 into each of the empty squares so that each digit appears exactly once in each row, column and 3x3 box. Wherever the number in the cell equals to a total of any amount of the closest numbers in any direction - there is an arrow pointing to that direction. Moreover on each marked main diagonal there are exactly three different digits.