Here is the second picross wich will give you the missing digits in the part 1.
So you can verify your grade in "sudomania"...

Please notice that this sudoku (of the part 1) has reached a score of 11,9 on the sudoku difficulty scale (from 1 to 12).
Till now, it's the most difficult ever known.

This difficulty is a bit staunting : in the grid of part 1, 21 digits are given.
And some sudokus with only 18 or 19 given digits are much easyer than this one.

So this is a small mystery about the quantity of digits given with a grid, wich participate to the difficulty leveL
And the mystery continues about grids with only 17 given digits.
Some mathematicians still work on the subject

Note : the summary tells you that there is many solutions. But putting logical white cells in the grid makes this sentence false : you can find the unique solution without any help.