Anyone who played minecraft should know this circuit, because it's pretty popular and also not that hard to make. The first man who remade this circuit to SC was laurensweyn. If someone doesn't know what it does - it has three inputs (switches ) and two outputs (lighbulbs ). When you switch any switch, lightbulb marked "1" will turn on. When you switch any two switches, lightbulb "2" will turn on and the "1" will turn off. And finaly, when you switch all the three switches, both lightbulbs will turn on (because 1+2=3).