Outline
Spherical sections of a 3-Sphere
The double orthogonal projection of the 3-sphere and its sections with a 3-space, plane, and line.
See https://link.springer.com/article/10.1007/s00004-017-0368-2 and https://link.springer.com/article/10.1007/s00004-018-0384-x for an introduction into the topic
