Logic Masters Deutschland e.V.

Rules

Place the numbers 1-4 in every cell so that no number repeats in any row, column, or bolded 2x2 box.

Cells separated by a knight’s move (in chess) do not contain the same digit.

The puzzle contains three invisible lines (you don’t necessarily need to find their exact paths to solve the puzzle):

-A high line, which only contains the digits 3 and 4,
-A low line, which only contains the digits 1 and 2,
-And a parity line, which must contain digits of the same parity

Lines may cross each other and move in any direction (including diagonally), but no line branches or revisits cells. If a line exists in a 4x4 region, then it must visit every 2x2 box in that region. The digits along all three lines sum to the same prime number.

Circles indicate cells that contain an endpoint of at least one line.

Link: https://sudokupad.app/t6hvnmjaz2