超立方体中子集的平均成对汉明距离
Average pairwise Hamming distance of a subset in a hypercube
Yijia Fang, Hao Huang
AI 速览:作者证明密度为1/8的{0,1}^n子集的平均成对汉明距离至少为(n-3)/2,且等号仅由(n-3)维子立方体达到。
In this note, we prove that for a subset $\mathcal{F}$ of $\{0,1\}^n$ of density $\frac{1}{8}$, its average pairwise Hamming distance is at least $\frac{n-3}{2}$, with equality attained only by $(n-3)$-dimensional subcubes. This answers a question of Lei Yu, and solves an important open case of a more general question posed by Ahlswede and Katona in 1977.