Given: a mesh which forms one-n'th of a torus. I Alt-D-duplicate it, rotate the copy by 360°/n, and get the ends to meet up. Repeat n-1 times.
I have now a nicely symmetric object which I can edit further. This is not the problem.
The problem is that when I move a vertex at the border between copies, that nice alignment is destroyed. Obviously I cannot join the corresponding vertices; it's the same underlying mesh, after all..
Thus, how can I keep them in sync while editing? Repeating the edit steps on the "other" side is tedious, and snap-to-vertex doesn't help much either.
To clarify: I want to create a closed object with n-fold symmetry which stays closed and symmetric, no matter which vertex/edge/face I move. A normal torus will not stay symmetric. A 1/nth-torus with n-1 360°/n-rotated copies will not stay closed when I move a vertex/edge/face at the border.