Best Approximation in ℝ-Trees
- 17 May 2007
- journal article
- research article
- Published by Informa UK Limited in Numerical Functional Analysis and Optimization
- Vol. 28 (5-6), 681-690
- https://doi.org/10.1080/01630560701348517
Abstract
An ℝ-tree is a geodesic space for which there is a unique arc joining any two of its points, and this arc is a metric segment. We give a constructive proof of the following “best approximation” theorem in such spaces. Suppose X is a closed convex and geodesically bounded subset of an ℝ-tree H, and suppose T:X → 2 H is a multivalued upper semicontinuous mapping whose values are nonempty closed convex subsets of X. Then there exists a point x 0 ∊ X such that We also give a topological version of the above theorem in a more abstract setting, and we prove a KKM theorem for geodesically bounded ℝ-trees.Keywords
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