Unweighted Code Sparsifiers and Thin Subgraphs

We show that for every $k$-dimensional linear code $\mathcal{C} \subseteq \mathbb{F}_2^n$ there exists a set $S\subseteq [n]$ of size at most $n/2+O(\sqrt{nk})$ such that the projection of $\mathcal{C}$ onto $S$ has distance at least $\frac12\mathrm{dist}(\mathcal{C})$. As a consequence we show that any connected graph $G$ with $m$ edges and $n$ vertices has at least $2^{m-(n-1)}$ many $1/2$-thin subgraphs.