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The great tunnel switch II (Posted on 2008-12-26) Difficulty: 3 of 5
There are 4 doors to the secret Truth Club room, each one at the end of a tunnel leading there. Each of the members has a keycard to a different door. All the doors are unlocked from the inside, but to enter from the outside, one needs to swipe the door's keycard to open the door for a few seconds.

You have found a copy of one of these cards, and want to prove beyond a reasonable doubt to the club members that you can unlock one of the doors, however, you don't want to expose to anyone whose door it is. What can you do to show this? (preferably with no additional materials, and without anybody else inside the cave/tunnels)

(Assume the club members are honorable enough to follow their part of the plan you propose.)

Here is a map of the tunnels:

A map of the tunnels

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re(4): possible solution -Oh that easy? | Comment 8 of 9 |
(In reply to re(3): possible solution -Oh that easy? by brianjn)

I have since located my reference which I had at the posting of the prior problem. 

I didn't properly understand it then.  And then this one.  Reading the reference I am now surprised that the "hotel corridor" thought was dismissed off-handedly, I can't see how that would have worked.  But then, without some "inside" knowledge (the reference) and even then????

"without anybody else inside the cave/tunnels"   I'm reading this as excluding me/you the demonstrator!  Or is this supposed to mean the demonstrator is excluded?
  Posted by brianjn on 2008-12-27 23:21:28

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