A *convex* polytope $P\subset\Bbb R^d$ is *centrally symmetric* if $-P=P$. It is *self-dual* (or better, self-polar?) if its polar dual $P^\circ$ is congruent to $P$, that is, there is a map $X\in\mathrm O(\smash{\Bbb R^d})$ with $\smash{P^\circ}=XP$. > **Question:** Are there centrally symmetric self-dual polytopes in dimension $d>4$? Such exist in dimension $d=2$ and $d=4$: - for $d=2$ we have the regular 2n-gons, - for $d=4$ we have the regular 24-cell. I do not know of any others.