Karlsson–Nussbaum boundary-limit conjecture for fixed-point-free maps

Let (Ω,δ)(\Omega,\delta) be a Hilbert geometry, let f ⁣:ΩΩf\colon\Omega\to\Omega be a fixed point free non-expansive mapping, and let ω(x,f)\omega(x,f) denote the set of limit points of the forward orbit of xx. A subset of Ω\partial\Omega is convex when it contains the line segment between any two of its points.

Karlsson–Nussbaum conjecture. There exists a convex set Λ\Lambda in Ω\partial\Omega such that

ω(x,f)Λfor all xΩ.\omega(x,f)\subseteq\Lambda\quad\text{for all }x\in\Omega.

This conjecture would constrain all orbit-limit sets of a fixed-point-free non-expansive map to a single convex subset of the boundary. The supplied text gives a counterexample showing that stronger statements about prescribed boundary limit sets fail, but does not report a resolution of this conjecture.

Sources & referencesView supporting material

Primary source

Bas Lemmens and Roger Nussbaum, “Birkhoff's version of Hilbert's metric and its applications in analysis”, arXiv:1304.7921 (2013).

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