Theoretically there should be a frontier hut, but there isn't a single customs official and the border has been unguarded for over 300 years.
The border doesn't need enforcement thanks to their set up. 
mnli hypothesis: The border doesn't need enforcement thanks to their set up.  premise: Theoretically there should be a frontier hut, but there isn't a single customs official and the border has been unguarded for over 300 years.