  Let P be a lattice polytope in R^n, and let P \cap Z^n = {v_1,...,v_N}. If
the N + \binom N2 points 2v_1,...,2v_N; v_1+v_2,...v_{N-1}+v_N are distinct, we
say that P is a "distinct pair-sum" or "dps" polytope. We show that, if P is a
dsp polytope in R^n, then N \le 2^n, and, for every n, we construct dps
polytopes in R^n which contain 2^n lattice points. We also discuss the relation
between dps polytopes and the study of sums of squares of real polynomials.
