At most nine lines in Euclidean three-space have pairwise distance one
arXiv:2606.22605
Abstract
J.E. Littlewood posed the question of how many infinite circular cylinders of unit radius can be arranged so that each touches all the others. We give a computer-free proof that one cannot find ten such cylinders. This improves a known result, namely that there are no eleven such cylinders, which was obtained making partial use of computer verification.
7 pages, 2 figures