There is a building with four floors. On the first floor,

There is a building with four floors. On the first floor, there
is a convention of architects. On the second floor, there is a
vinyl manufacturing plant. On the third floor there is a fast food
stand, and on the fourth floor there is a library.

Q: What would happen if a librarian traveled down in a small
elevator with one other person from each floor?
A: The elevator would be full.