4. Inclusion-Exclusion. A town of n citizens has a cinema with seating capacity less than n. Over the weekend three different films are shown (once each). Each citizen can watch as many of the films as they want. Assume that, for every pair of citizens, there is at least one film that they both watch. Prove that for at least one of the films, someone is sitting on the floor (i.e. the film is overcapacity). 4. Inclusion-Exclusion. A town of n citizens has a cinema with seating capacity less than n. Over the weekend three different films are shown (once each). Each citizen can watch as many of the films as they want. Assume that, for every pair of citizens, there is at least one film that they both watch. Prove that for at least one of the films, someone is sitting on the floor (i.e. the film is overcapacity)