Random Stuff > High Stakes
You are given two wooden stakes, and a single loop of rope. The stakes are hammered into the ground vertically, a certain distance apart. It is possible to loop the rope around the stakes such that it cannot be removed by pulling it horizontally. One example of how this can be done viewed from above is:
The problem is to satisfy the above requirement in such a way that when either of the two stakes is removed, the rope can then be pulled away horizontally. (The configuration drawn above is not good enough, as the rope will still be looped around one stake even when the other has been removed.) The second part of the problem is to achieve the same for any number of stakes - when any single stake is removed, it should be possible to remove the rope by pulling horizontally.
Here's a solution for the case of 2 and 3 posts, respectively:
This solution can be generalised to an arbitrary number of posts as follows. Note that the three ends of rope at the left edge of the diagram join directly onto the three ends of the rope at the right edge.