Any nontrivial, closed, simple, smooth spherical curve dividing the surface of a sphere into two parts of equal areas has at least four inflection points.
Tennis Ball Theorem
See also
Ball, Baseball Cover, Inflection Point, Spherical CurveExplore with Wolfram|Alpha
References
Arnold, V. I. Topological Invariants of Plane Curves and Caustics. Providence, RI: Amer. Math. Soc., 1994.Martinez-Maure, Y. "A Note on the Tennis Ball Theorem." Amer. Math. Monthly 103, 338-340, 1996.Referenced on Wolfram|Alpha
Tennis Ball TheoremCite this as:
Weisstein, Eric W. "Tennis Ball Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/TennisBallTheorem.html