At my workplace there's a room with two entrances, each featuring a push button light switch, A and B. There are two ceiling mounted lights, 1 and 2.
Switch A switches both lights on/off. Funny enough, if both lights are on, switch B switches off a single light (2). Now in this state, switch A "flips" the state of the two lights (2 goes on, 1 goes off).
SWA==on AND SWB==on ==> Light1==on AND Light2==on SWA==off AND SWB==on ==> Light1==off AND Light2==off SWA==on AND SWB==off ==> Light1==on AND Light2==off SWA==off AND SWB==off ==> Light1==off AND Light2==on
I don't know if these are 3-way or 4-way switches.
Just out of academic curiosity: how exactly is this - obviously flawed - circuit possibly implemented?
(Disclaimer: I'm a physician, not any kind of engineer)