Another, more topological example of an intrinsic property of a manifold is the Euler characteristic. For a non-intersecting graph in the Euclidean plane, with "V" vertices (or corners), "E" edges and "F" faces (counting the exterior) Euler showed that "V"-"E"+"F"= 2. Thus 2 is called the Euler characteristic of the plane. By contrast, in 1813 Antoine-Jean Lhuilier showed that the Euler characteristic of the torus is 0, since the complete graph on seven points can be embedded into the torus. The Euler characteristic of other surfaces is a useful topological invariant, which has been extended to higher dimensions using Betti numbers. In the mid nineteenth century, the Gauss–Bonnet theorem linked the Euler characteristic to the Gaussian curvature.