<P> A principal vertex x of a simple polygon P is called an ear if the diagonal (x, x) that bridges x lies entirely in P. (see also convex polygon) According to the two ears theorem, every simple polygon has at least two ears . </P> <P> A principal vertex x of a simple polygon P is called a mouth if the diagonal (x, x) lies outside the boundary of P . </P> <P> Any convex polyhedron's surface has Euler characteristic </P> <Dl> <Dd> V − E + F = 2, (\ displaystyle V - E + F = 2,) </Dd> </Dl>

What is the difference between a vertex and a corner