Logic Masters Deutschland e.V.

Rules:

• Normal sudoku rules apply.
• Digits in a cage cannot repeat and sum to the small number in its corner.
• Digits separated by a knight's move (in chess) cannot sum to 9.
• Red lines are reduction lines. A red line cannot contain its reduction value, which is calculated as follows:
  1. Sum the digits on the line.
  2. If the total is a two digit number, sum the digits of that number. Repeat this step until you get a single digit number.

  Example: The sequence 2,5,7 sums to 14, which sums to 5, therefore the sequence 2,5,7 cannot fill a red line.

Link: SudokuPad