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Topic: [Help] Loop and Vest Puzzle
Message: Posted by: ipe (Feb 1, 2019 03:43AM)
There is a fascinating puzzle I cannot solve even with the solution! And the more I think about it and the more it looks impossible!

Problem:
You can do this by yourself, but it is much easier to use a volunteer. The volunteer puts on the vest (zipping/snapping/buttoning it up). The volunteer places the loop over one arm, and puts that hand on that arm in the vest pocket. The problem solver must now remove the loop without the volunteer removing his hand from his pocket, and without passing the loop over this hand.

Solution:
Push the loop through the arm hole of the vest, out of the neck hole, over the volunteer’s head, down through the neck hole and out the other arm hole, around the volunteer’s other hand, and back into the vest. If you did this correctly, the loop should now be around the volunteer’s chest, under the armpits. So you can just pull it down to the feet, and the volunteer can step right out.
[Source: http://www.dehn.wustl.edu/~blake/circles/talks/2012-Mar04-Holly_Bernstein-Topology_Puzzles.pdf]

You can find a pictorial presentation of the problem here, under the name "People Puzzle 2": https://books.google.it/books?id=Y23Zpck2TnMC&pg=PA295&lpg=PA295&dq=puzzle+rope+loop+arm+hand+in+your+pocket+get+it+out&source=bl&ots=ADEKD5YvbB&sig=ACfU3U2dvsEpPtLSvDAlpnTf-t38xes6FQ&hl=it&sa=X&ved=2ahUKEwiAha7ej5rgAhWvMewKHWGABeIQ6AEwEXoECAIQAQ#v=onepage&q=puzzle%20rope%20loop%20arm%20hand%20in%20your%20pocket%20get%20it%20out&f=false


I have another wording for the problem and the solution from Abbott's Encyclopedia of Rope Tricks for Magicians.

Problem: use a soft rope about nine feet long and tie the ends together. Remove your coat, put the loop of the rope over your right arm and put your right hand in your vest pocket. Have anyone try to get it off without untying or cutting the rope and without you removing your hand from vest pocket.

Solution: pull the loop through the armhole of your vest, over your head, out through the other armhole and over the other arm. You can now reach up under vest and pull the rope down. It will fall to the floor, leaving you only to step out of it and be free.


Can you help me to understand the solution? Thank you. :bg:
Message: Posted by: lnlver (Feb 4, 2019 08:48AM)
You can understand how this works by studying topology. By morphing the vest and loop, you can show that in their original positions in the puzzle, they were completely separate.
Message: Posted by: ipe (Feb 13, 2019 07:14AM)
Hi lnlver, thank you for your reply.

Could you rephrase the solution to this puzzle? Maybe, with a different wording I will be able to understand it (I'm not an English mother tongue).
Message: Posted by: ddyment (Feb 13, 2019 09:55AM)
If you are having trouble, it's probably because the instructions themselves are unclear as to direction.

Begin by putting the loop through one armhole of your vest, [b]from the sleeve side to the neck side[/b].

Then pull it through the neck hole, and loop it over your head.

Then put it through the other vest armhole, [b]from the neck side to the sleeve side[/b].

Then loop it over your hand, and you are essentially free.
Message: Posted by: lnlver (Feb 18, 2019 09:25AM)
[quote]Could you rephrase the solution to this puzzle? Maybe, with a different wording I will be able to understand it (I'm not an English mother tongue).[/quote]
In simple terms, from a topological standpoint, the loop was really never inside the vest.

In topology, a doughnut is equivalent to a coffee cup; they each have a single hole in their shape. You can distort the coffee cup to get a doughnut and vice versa.
Message: Posted by: alicauchy (Feb 19, 2019 11:17AM)
[quote]On Feb 18, 2019, lnlver wrote:
In simple terms, from a topological standpoint, the loop was really never inside the vest.
[/quote]

You are right. However, your statement only explains *why* the trick has a solution but not *how* it works.
Message: Posted by: ipe (Feb 26, 2019 03:34AM)
Alicauchy, you are right. I perfectly understand the theory, but it the how the problem. :)

Doug, thank you for the very useful explanation. It is clear now. ;)