Puzzle/maths problem

[glenatron]

Emperor Alexius of Barzantium has six most trusted advisors in his cabinet: Bericus, Constantine, Davidius, Esquilinus, Fabius and Gesius. One of them however is a traitor, spying for the rival empress Zoe of Foobia. Alexius knows that any of his own agents that empress Zoe is aware of will be executed, but as a question of security he likes to keep the identities of his agents secret from everyone. He knows he will have to give away some of them in order to identify the spy. What is the smallest number of agents he can betray to definitely identify the spy?

This isn't a standard puzzle question really (or at least, it is, but I'm not setting it as a puzzle ) it's more a fundamental maths/computer science question that I feel should be intuitively obvious to me and is probably about the underlying principles behind bitmasking or parity that I've never really explored far enough to master. So assuming this is a standard question does anyone know what it is called? If it is not a standard question does anyone have any interesting answers to it? I feel there should be a solution that gives away no more than three spies, but I haven't yet found my way to it.

Comments

[life-of-tom.livejournal.com]

what if you tell four people?

then either he dies, and you're searching a group of four or he lives and you're searching a group of two.


group of two- tell one of them. Bada bing, you get to use just one spy.

group of four- tell two about a second spy, you might be lucky and only have to give him away or you might need to sacrifice the third?

No way like that apart from hoping you get lucky.