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.
It is commonplace to have a frontier hut. 
mnli hypothesis: It is commonplace to have a frontier hut.  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.