Logic Masters Deutschland e.V.

While tinkering with a different puzzle, I discovered some interesting facts about placing 2x2s into 3x3s—and to solve this puzzle, you must discover those facts as well. Many thanks to Loric and Pokitchayng for testing and feedback.

Rules:

Normal Sudoku: Place the digits 1 to 9 in every row, column, and 3x3 box.

Whisper Squares:

• Every 3x3 box contains one hidden 2x2 region called a Whisper Square.
• In a Whisper Square, orthogonally adjacent digits must have a difference of 5 or greater.
• Whisper Squares must not touch orthogonally, but they may touch diagonally.

Equal Sum Cages: Within each cage, the sum of digits inside Whisper Squares equals the sum of digits outside Whisper Squares.

Here are some examples:

And here is the puzzle. You can solve online:

• CTC
• F-Puzzles

For anyone interested, I posted a video (in English) with a walkthrough of the break-in here. The first few minutes includes an explanation of the rules.