4 switch activation system

So my friend Cloaca asked me to com up with a way to hit 4 switches in any random order, but that once all were hit, that something like a door, or a piston or some other machine could activate. I came up with the base and he figured out a better reset system for it then i had originally. this is something he wanted for an adventure map where a person could level up or even for a PVP arena type thing. so this one is put forth in a linear fashion, but i'm sure can easily be arranged in any fashion for your adventure map.
World save now uploaded.

i also added in a starter adventure maze to give an idea of possible use's.