Logic Masters Deutschland e.V.

Rules:

Normal sudoku, German Whisper, Dutch Whisper and Kropki (black) rules apply. Digits separated by an orange dot differ by exactly 4. Not all orange dots are necessarily given.

Hope you enjoy!

SudokuPad

HINT1:

A good question to consider is, "Where can the digit 5 be on an orange?" A key step is to prove that r4c1 and r4c3 cannot be 5.

HINT2:

The black kropki dot is the only clue that breaks the symmetry between large and small numbers (between X and 10-X). Unfortunately it is only used at the very end. Try breaking the symmetry at the beginning, even though it may not be correct.

Note:

The orange dot in column 9 can be removed, and the puzzle can still be solved logically. In fact, this puzzle has a unique solution without all three orange dots! However, I couldn't solve it without any dot in box 7. If you find a way to do so, please let me know!