%0 Journal Article
%T Topology of geometric joins
%A Imre Barany
%A Andreas F. Holmsen
%A Roman Karasev
%J Mathematics
%D 2013
%I arXiv
%R 10.1007/s00454-015-9665-2
%X We consider the geometric join of a family of subsets of the Euclidean space. This is a construction frequently used in the (colorful) Carath\'eodory and Tverberg theorems, and their relatives. We conjecture that when the family has at least $d+1$ sets, where $d$ is the dimension of the space, then the geometric join is contractible. We are able to prove this when $d$ equals $2$ and $3$, while for larger $d$ we show that the geometric join is contractible provided the number of sets is quadratic in $d$. We also consider a matroid generalization of geometric joins and provide similar bounds in this case.
%U http://arxiv.org/abs/1309.0920v4