Proving Hall's marriage theorem using Sperner's lemma

Penny Haxell's 2011 paper On Forming Committees in the American Mathematical Monthly explicitly uses Sperner's lemma to prove Hall's theorem for bipartite graphs (see theorem 4.1 and 4.2).


In addition to Carlo Beenakker's answer that gives Hall via Sperner directly, I think you can also get it by applying Hall's Theorem for Hypergraphs as follows. Let $G$ be a bipartite graph with partite sets $X, Y$, and write $V(X) = \{x_1, \ldots, x_n\}$. For each $i$, define a $1$-uniform hypergraph $H_i$ with vertex set $N(x_i)$ and edge set $\{ \{y\} : y \in N(x_i) \}$.

Letting $\mathcal{A} = \{H_1, \ldots, H_n\}$, we see that $\mathcal{A}$ has a disjoint set of representatives if and only if $G$ has a matching that saturates $X$. Now the condition of Aharoni and Haxell's Theorem 1.1 applied to the family $\mathcal{A}$ is clearly equivalent to Hall's Condition on $G$. Since classical Hall's Theorem falls out of the hypergraph version so quickly, I think it's fair to think of the topological proof of the hypergraph version as also being a topological proof of Hall's theorem.