Logic Masters Deutschland e.V.

• Normal sudoku rules apply.
• Dutch Flatmates: Every 5 in the grid must have a 1 directly above it, or a 9 directly below it. It may have both, but it doesn't need both.
• Global Modulo 3: Every 2x2 region must have digits of all three residue classes modulo 3, i.e. one of each of the sets 147, 258, 369.
• Digits in a circle clue must appear at least once in one of the four surrounding cells.

Online in Sudokupad

See also:

• dissipation gradation
• one more lonely bird