Computable fixed-point selection for nonexpansive mappings on two-dimensional Banach spaces

Let EE be a uniformly convex, smooth, computable Banach space of dimension two, and let KEK\subseteq E be bounded, convex, and located, meaning that its distance function is computable. Write Kco(K){}\mathcal{K}^{\operatorname{co}}(K)\setminus\{\emptyset\} for the represented space of nonempty co-semi-decidable convex subsets of KK, and N(K)\operatorname{\mathcal{N}}(K) for the relevant space of nonexpansive self-mappings of KK. Computable fixed-point selection conjecture. The multi-valued mapping

Fix1 ⁣:Kco(K){}N(K)\operatorname{Fix}^{-1}\colon \mathcal{K}^{\operatorname{co}}(K)\setminus\{\emptyset\}\rightrightarrows \operatorname{\mathcal{N}}(K)

is computable. This is presented as a possible generalisation of the preceding two-dimensional Hilbert-space result to uniformly convex and smooth real Banach spaces. The source gives no resolution evidence for this claim, so its status remains open.

Sources & referencesView supporting material

Primary source

Eike Neumann, “Computational Problems in Metric Fixed Point Theory and their Weihrauch Degrees”, arXiv:1506.05127 (2015).

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