There is a panel containing 3 light switches in front of you. Each switch controls a light in a room somewhere. Doesn't really matter where. You can play with the switches as much as you like, but you're only allowed to enter the room once. How do you tell which switch controls which light? Again, you can only enter the room once, so you cannot play with the switches after you enter the room, but you can play with them as much as you want before you enter the room. One entry is all it takes to determine which switch controls which light.
