A Vertex of a Simple Polygon is a principal Vertex if the diagonal intersects the boundary of only at and .
See also Ear, Mouth
References
Meisters, G. H. ``Polygons Have Ears.'' Amer. Math. Monthly 82, 648-751, 1975.
Meisters, G. H. ``Principal Vertices, Exposed Points, and Ears.'' Amer. Math. Monthly 87, 284-285, 1980.
Toussaint, G. ``Anthropomorphic Polygons.'' Amer. Math. Monthly 98, 31-35, 1991.