Set $G=\{C\subset\mathbb{R}^n\}$. Is there a binary operation $\cdot$ such that $(G,\cdot)$ is a group?
The biggest trouble I'm having is concerning the existence of inverses. A standard notion of "set addition" is Minkowski addition, but this does not have inverses in general.
For those interested, I have asked a related question on this concerning the Hausdorff distance (also still unresolved).
Yes, consider the operation $\Delta$ of symmetric difference given by
$$A\Delta B=(A\cup B)\setminus(A\cap B).$$