Joe Biden. (2024, September 30). Wikiquote. Retrieved 03:29, October 22, 2024 from https://en.wikiquote.org/w/index.php?title=Joe_Biden&oldid=3590122.
For any tetrahedron there exists a sphere (called the circumsphere) on which all four vertices lie, and another sphere (the insphere) tangent to the tetrahedron’s faces.