Imagine that you need to assemble a structure, such as the one depicted on the cover of this magazine. The pieces would need to be joined together, one at a time, until the structure is complete. To do this, you would choose a starting point and then add one piece at a time. You might find out, however, that, as you assemble the structure, some kind of external support is needed since the intermediate structures are not as rigid as the completed structure. You might wonder, then, whether there is a way to assemble the structure so that all of the intermediate structures are inherently rigid. The reverse problem is also of interest: How do you take the structure apart so that it doesn't collapse in the process?