Schoenflies problem

The Schoenflies problem is a question in the field of topology, specifically concerning the embedding of spheres in Euclidean spaces. It is named after the mathematician Rudolf Schoenflies. The problem essentially asks whether every simple, closed curve in three-dimensional space can be "filled in" by a disk, or in more technical terms, whether every homeomorphism of the 2-sphere (the surface of a solid ball) can be extended to a homeomorphism of the solid ball itself.