Okay, you go up to one of them and say "Would he (i.e. the other guy) tell me that this door leads to Heaven?" If he says "no" go through it. This is headwrecking, but I think it works. If it IS the door to heaven and you're asking the liar then you're okay, and if it IS the door to heaven and you're asking the truth person it's okay. Just don't go through the one they say yes to. Is that it, or am I way off...?