Another puzzle: There is a light bulb and a consciousness switching machine. Two people can enter the machine and switch their consciousness. Whenever two people switch their consciousness, the light bulb switches (on->off and off->on). You have access to as many people as you want. The light bulb starts off being off. Is it possible to using the machine in such a way that in the end, everyone's consciouness is back to where it started but the light bulb is on. If yes, give a method how to do it, and if not, explain why.
