arXiv · 2009.09522
We give another proof of Toyoda's theorem that describes 5-point subpaces in CAT(0) length spaces
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Nina Lebedeva, Anton Petrunin. 2022-06-29. 5-point CAT(0) spaces after Tetsu Toyoda. https://doi.org/10.1515/agms-2020-0126
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We prove that every finite-dimensional Busemann \(G\)-space of dimension at least five has the disjoint disks property (DDP). For a sufficiently small metric sphere \(L=S(c,r)\), we show that every embedded arc contained in an exact distance level is a homotopical \(Z_2\)-set in \(L\). It follows that \(L\) has the disjoint arc-disk property and the disjoint homotopies property. Daverman's product theorem then gives DDP for \(L\times\mathbb R\), and a local avoidance argument at the center yields DDP for the ambient \(G\)-space. Since finite-dimensional Busemann \(G\)-spaces are generalized manifolds, in dimensions at least five the remaining obstruction to the Busemann conjecture is the resolution problem.
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