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arXiv · 2511.20345

An improvement of the Blanco-Koldobsky-Turn\v{s}ek characterization of isometries

Jayanta Manna·Kalidas Mandal·Kallol Paul·Debmalya Sain
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Abstract

We present an improvement of the Blanco-Koldobsky-Turn\v{s}ek characterization of isometries in normed linear spaces by using the concept of level vectors of an operator. In this context, we characterize level vectors entirely through directional preservation of Birkhoff-James orthogonality and analyze the associated geometric and structural phenomena that they induce. Furthermore, in spaces whose unit balls possess the \textit{Krein-Milman property}, we derive an additional refinement of the Blanco-Koldobsky-Turn\v{s}ek characterization of isometries.

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Jayanta Manna, Kalidas Mandal, Kallol Paul, Debmalya Sain. 2025-11-25. An improvement of the Blanco-Koldobsky-Turn\v{s}ek characterization of isometries. https://arxiv.org/abs/2511.20345

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