A geometric Hall-type theorem

Abstract:

We introduce a geometric generalization of Hall’s marriage theorem. For any family $F = \{X_1, \dots , X_m\}$ of finite sets in $\mathbb {R}^d$, we give conditions under which it is possible to choose a point $x_i\in X_i$ for every $1\leq i \leq m$ in such a way that the points $\{x_1,\dots ,x_m\}\subset \mathbb {R}^d$ are in general position. We give two proofs, one elementary proof requiring slightly stronger conditions, and one proof using topological techniques in the spirit of Aharoni and Haxell’s celebrated generalization of Hall’s theorem.