  A finite abstract simplicial complex G defines a matrix L, where L(x,y)=1 if
two simplicies x,y in G intersect and where L(x,y)=0 if they don't. This matrix
is always unimodular so that the inverse g of L has integer entries g(x,y). In
analogy to Laplacians on Euclidean spaces, these Green function entries define
a potential energy between two simplices x,y. We prove that the total energy
summing all matrix elements g(x,y) is equal to the Euler characteristic X(G) of
G and that the number of positive minus the number of negative eigenvalues of L
is equal to X(G).
