Wolfgang: Not necessarily. Without the "yes" or "no" restriction, the liar could respond by saying, "He [the truthful twin] won't respond because he's deaf"! The truthful twin could respond by saying, "He'll tell you to go to hell!" You also must be careful when using the phrase "your brother"; perhaps these two have other brothers! Better be careful with the word "respond", too; without the "yes" or "no" restriction, the liar could respond by giving you the finger.

Your question would have to be more specific: "If I ask the other guard in this room to tell me only whether door 'A' leads to Heaven or Hell, and to give me no other responses, will he say 'Heaven' or will he say 'Hell'?" That might work.... except that either twin could answer that one with "yes"! Besides, doesn't that "and" clause constitute a second question?*G*

I guess the question would have to be: "If I ask the other guard in this room to tell me only whether door 'A' leads to Heaven by giving me no other response except to say 'yes' or 'no', will he say 'yes'?" Anybody see any loopholes there?

So is this supposed to be a riddle of logic, or semantics? Both?