4 ms·

Topologically the hollow torus is more interesting, the solid one is effectively a slightly thicker circle.

• deleted 4y ago
  [deleted]
• sterlind 4y ago
  I was very confused until I realized you meant the boundary of a circle, not a filled circle.
  • Sharlin 4y ago
    A filled circle is called a disk (or 2-ball) in math.