Quote Originally Posted by Carôusoul View Post
But you're talking about it?


So it is a concept, and nothing more.
We talk about two different rectangles, and that they share a side. Drawing such a diagram, we see the shared side is no longer a side at all.

Now, they "share a side", and thus: They're united as one larger rectangle, and the sides disappear into each other. Thus, the sides no longer exist, and thus, no line to be drawn, unless we reconsider them as separate.