Zoll surface

A Zoll surface is a mathematical surface which is named after the German mathematician Ernst Zoll. It has the property that any two points on the surface are the same distance away from each other. This surface looks like a sphere that is squished at the top and the bottom. To make it easier to imagine, imagine a big beach ball with the top and bottom part very slightly squished. This makes the Zoll surface look like a round dome shape.