## The Ultimate Riddle

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More riddles on this site:

Two math riddles

Greg’s dinosaur riddle

A riddle

The mystery beeping riddle

What can the scond prize possibly be

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### 15 Responses to The Ultimate Riddle

1. Gil, whom did you hear this from?

I assume it was recently, and just wondered whether it’s got anything to do with me showing this trick to several mathematicians in a conference last May.

2. daveagp says:

There is a related trick I learned of in grad school: tie both of your shoe laces together, then you have to turn your pants inside out. I am grad that one is not available on YouTube!

3. Gil Kalai says:

Ori, well, I remember a dinner 7-10 years ago at New Haven with John Conway demonstrating it and Hillel Furstenberg trying to repeat it, but I think I already knew this even before the dinner. I dont remember for sure.

4. Gil says:

Is there a simple explanation why when you do it one way it works and when you do it the other way it does not work?

5. Ori says:

Gil: just wondering whether it was a coincidence.

6. Gil says:

Dear Ori, Coincidences is a tricky subject to study and even to define. (But extremely interesting and rather important.) Whom did you hear this trick from?

7. Ori says:

Gil: I’ve known it since childhood, perhaps from my father, I should ask him.

8. Gil says:

Ori, Do you think this trick has a mathematical flavour?

9. Ori says:

I don’t know about flavor, but it certainly has mathematical aspects.

GK: What aspects?

10. Tom says:

The simplest way I can explain it is: when you are touching your nose, your arms are crossed and one of them is on top (say the left one). In order for the trick to succeed, the left index finger must be on top of the right index finger. Thus, when you start the trick, you mix your fingers in such a way that the left index finger is below the right one, and it will come up on top when you twist.

11. Tom says:

Equivalently, if the left (resp. right) arm is lower when you start the trick, then the left index finger (resp. right) must also be lower.

12. Ori says:

A related trick (and afterward the coolest card trick ever).

13. jonas says:

To daveagp: can’t you just take off your shoes with the laces still tied?