Normal sudoku rules apply. Digits on the line must be consecutive. For example, a 4 must be followed by either a 3 or a 5, and a 1 must be followed by a 2.
Here's a hint if you're having trouble breaking into the puzzle:
There are four cells (r37c37) that are consecutive with four other digits. You can check that if two of these cells are in the same row or column, they cannot have a difference of 1 or 2.
Lösungscode: Row 1 and column 9 (18 digits).