English

Adding a point to configurations in closed balls

Geometric Topology 2019-05-09 v2

Abstract

We answer the question of when a new point can be added in a continuous way to configurations of nn distinct points in a closed ball of arbitrary dimension. We show that this is possible given an ordered configuration of nn points if and only if n1n \neq 1. On the other hand, when the points are not ordered and the dimension of the ball is at least 2, a point can be added continuously if and only if n=2n = 2. These results generalize the Brouwer fixed-point theorem, which gives the negative answer when n=1n=1. We also show that when n=2n=2, there is a unique solution to both the ordered and unordered versions of the problem up to homotopy.

Keywords

Cite

@article{arxiv.1809.06946,
  title  = {Adding a point to configurations in closed balls},
  author = {Lei Chen and Nir Gadish and Justin Lanier},
  journal= {arXiv preprint arXiv:1809.06946},
  year   = {2019}
}

Comments

6 pages; simplified proof of Theorem B and added proof of uniqueness for the case $n=2$ as Theorem C

R2 v1 2026-06-23T04:10:50.972Z