Except for triangles, every simple polygon has at least two nonoverlapping ears.
Two-Ears Theorem
See also
Ear, One-Mouth Theorem, Principal VertexExplore with Wolfram|Alpha
References
de Berg, M.; van Kreveld, M.; Overmans, M.; and Schwarzkopf, O. Computational Geometry: Algorithms and Applications, 2nd rev. ed. Berlin: Springer-Verlag, p. 59, 2000.Meisters, G. H. "Principal Vertices, Exposed Points, and Ears." Amer. Math. Monthly 87, 284-285, 1980.Toussaint, G. "Anthropomorphic Polygons." Amer. Math. Monthly 122, 31-35, 1991.Referenced on Wolfram|Alpha
Two-Ears TheoremCite this as:
Weisstein, Eric W. "Two-Ears Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Two-EarsTheorem.html