On Jan 31, 2014, at 2:38 PM, Neighbor <email@example.com> wrote:
>> The funny thing that happens is that if *both* ends >> have that "drop of glue" on the end, you cannot get >> them to "stick together". > > I'd like to have an explanation of why we cannot, and then after hearing what's the reason, we will see how to proceed.
You are thinking of two equal line segments, which is fine, and in such case, they both have the ?common" end point in their sets. When you combine them you are then taking the union of the two sets, which results in only one instance of the common end point.