Although much exists in Wikipedia. I find that you can learn a lot when you let yourself get inspired by simple word combinations.
The trick is not to let yourself down thinking. This can not exist. Someone else can get inspired and figure out something important.
So I guessed that maybe there exist something like a Pi room. From what I know Pi is a constant. A room is a container and a container is kind of a set. Thats good enough for making a Pi room a potential rewarding guess.
If there exist a set that is like a room. Then maybe it can be an on/off set. That is if the room has a door.
So from this I speculate that maybe there exist on and off sets.