It's like the halting problem. It's hard to decide whether a given switch works in the general case. But it's possible to design an obviously correct breaker.

It's like the halting problem. It's hard to decide whether a given switch works in the general case. But it's possible to design an obviously correct breaker. Edit: the gnarly thing might be ensuring it doesn't harvest power through data wires or store power in covert capacitors or batteries.