=1/ The Konzerthaus in Berlin sells tickets known as Nacheinlasskarten, thirty minutes before the start of every concert that has been sold out.

Buyers of these tickets wait at the doors giving access to the various categories of seats in the concert hall. Thirty seconds before the concert starts, they are allowed in and can occupy any free seat. If there are no free seats they have to leave the hall and are not allowed to try again for a different category of seat (in any event, the conductor has already raised his baton). If the legitimate ticket holder for the seat arrives before the concert starts, the holder of the Nacheinlasskart must give up his/her seat and leave the hall.

What is your view of this type of ticket? Be as specific as possible. Careful! This is a lot more complicated than you probably think it is.