KKM meets colorful Carathéodory

Source abstract

The colorful Carathéodory theorem states that if $V_1,\dots,V_{d+1}\subset\mathbb R^d$ satisfy $0\in\mathrm{conv}\;V_i$ for every $i$, then there exist points $v_i\in V_i$ such that $0\in\mathrm{conv}\;\{v_1,\dots,v_{d+1}\}$. We give a new proof based on triangulations and the classical KKM lemma. We lift the sets $V_i$ to parallel affine copies of $\mathbb R^d$ in $\mathbb R^d\times\mathbb R^d$ and use a triangulation of the resulting point configuration to construct a KKM cover. Using the same approach, we prove the very colorful Carathéodory theorem.