This paper is to provide some new generalizations of the Pick Theorem. We first derive a point-set version of the Pick Theorem for an arbitrary bounded lattice polyhedron, then using the idea of weight function of [2] to obtain a weighted version; other Pick type theorems known to the author for integral lattice Z 2 are reduced to some special cases of the generalization. Finally, using the idea of Ehrhart [6] and the Pick Theorem, we give a direct proof of the reciprocity law for Dedekind sums. The ideas and methods presented here may be pushed to higher dimensions.
Point-Set Version of the Pick TheoremLet P be a lattice polygon of R 2 , i.e., the vertices of P are points of the integral lattice Z 2 . Let i(P ) be the number of lattice points of P and i(∂P ) the number of lattice points of its boundary ∂σ. The Pick Theorem says thatGiven a bounded lattice polyhedron X of R 2 ; we denote byX the closure of X and by int X the interior of X; the frontier of X is the setX − intX. The link of X near a point x ∈X is the intersection of X and a circle S 1 (x, r) centered at x with small enough radius r; the Euler characteristic χ(lk (x, X)) is a local topological invariant, which plays an important role in our Pick type theorems. For an interior point x ∈ int X, the link lk (x, X) is a circle and has Euler characteristic zero. If X is closed, then for any x ∈ fr X, the link lk (x, X) is a collection of finite number of arcs and points, so χ(lk (x, X)) = the number of branches near x.