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Exterior power sums

Yanping Luo, Ruiyi Yang, Keheng Zhu

math.CO Jul 24, 2026 · v1 math.NT
A separate Lean 4 development checking the solution of Erdős Problem 973 is provided in a linked GitHub repository, possibly with remaining axioms.
We prove that for every fixed $λ>0$ and all sufficiently large $n$, any $z_1,\dots,z_n\in\C$ with $|z_j|\geq1$ satisfy $\max_{2\leq k\leq n+1}|\sum_j z_j^k|>e^{-λn}$. Consequently, the $n$th root of the optimal maximum tends to $1$, so no constant $C>1$ in Erdős 973 can exist. The proof combines a truncated exponential factorization with overconvergence on an open set outside the unit disk and a normal-family obstruction for Cauchy transforms.

Erdős Problem 973 asks whether there is a constant C>1 such that points z_j with |z_j|>=1 (and z_1=1) can make max_{2<=k<=n+1}|sum z_j^k| smaller than C^{-n}. The question was recorded as open.

The proof argues by contradiction. It writes F(t)=prod(1-z_j t) as an exponential times a coefficient-small perturbation and uses the resulting coefficient identities to bound the normalized first power sum. It then shows overconvergence of truncated exponentials on an open disk outside the unit disk. Finally, Montel's theorem and the identity theorem show that a Cauchy transform cannot converge to a nonzero constant there. A Lean 4 development accompanies the paper, with its verification extent given by the declarations and remaining axioms in the repository.

For every λ>0 and all sufficiently large n, the maximum exceeds e^{-λn}. So the nth root of the optimal maximum tends to 1, and no constant C>1 exists, which answers Erdős 973 negatively.