Once in employment held a fun test of intelligence. Test that the move did not pass, because they do not runs out of time, but decided.
1. There are two buildings
2. Between the two buildings laid cable connection consists of three cores
3. Each building has a bell (220) and a button with a normally-open contact
4. To the right, the building is supplied with two wires (220V and neutral)
Formulation of the problem:
How to lay the wiring diagram inside the two buildings, so that when you click on the button in the left building, sounded the call to the right of the building, then the other way around?