Gates & Angels - A Tougher Version

[Falk Fish]

I guess that most of you know the riddle with the two gates and two angels
(out of which one is a liar and one a truthteller). Well, I have a tougher
version of this riddle and here it is:

"You are standing in front of two gates, one leading to heaven and the other
to hell, but you do not know which is which. Beside you are two angels, and
every angel can either tell the truth all the times or always lie. Every angel
knows where each door leads to, and the other angel's character. You can ask
one of the angels a single question, in order to find out what door you should
take. What will this question be?"

You can find the answer after the space of the few pages.
(Hint: It is based on the same concept as the original riddle)

BTW, does anybody know from where the original riddle originated? As far as I
know, it first appeared in the movie Labirinth. If you know of an older
appearance, mail me, or write an answer article, if it wouldn't be much of a
trouble.

ANSWER:
Ask one of the angles: "If I asked the other angle what you would answer if
I asked you what he would answer if I asked him if the left gate leads to
heaven, what would he answer?". His answer will always be the truth, so if
he answers "yes", take the left gate and if he answers "no", take the
right one. (unless you want to end up in hell.)

EXPLANATION:
The question is built in a way that every angle reports the true answer
to the question "Does the left gate lead to heaven?" twice. Therefore, even
if he is a lier, he will lie twice and so overall not change his answer.

--
Written by Shlomi Fish, ila...@datasrv.co.il
WARNING: Any similiarity between what was written in this article to real
life is definetly coincidential since it was stolen from the most