Upper bounds for the size of set systems with a symmetric set of Hamming distances

Abstract

Let $\mbox{$\cal F$}\subseteq 2^{[n]}$ be a fixed family of subsets. Let $D(\mbox{$\cal F$})$ stand for the following set of Hamming distances: $$ D(\mbox{$\cal F$}):=\{d_H(F,G):~ F, G\in \mbox{$\cal F$},\ F\neq G\}. $$ $\mbox{$\cal F$}$ is said to be a Hamming symmetric family, if $d\in D(\mbox{$\cal F$})$ implies $n-d\in D(\mbox{$\cal F$})$ for each $d\in D(\mbox{$\cal F$})$. We give sharp upper bounds for the size of Hamming symmetric families. Our proof is based on the linear algebra bound method.