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Characterizing the Daugavet property by squares of rank-one operators
Abstract
We prove that, for real Banach spaces of dimension greater than one, each of the identities |Id+T2|=1+|T2| and |Id−T2|=1+|T2|, required for every rank-one operator T, characterizes the Daugavet property, thereby answering a question posed by Kadets, Martín, and Merí (2007). Consequently, every extremely non-complex Banach space of dimension greater than one has the Daugavet property, answering a question of Martín and Merí (2011). We also compare pointwise versions of the square Daugavet properties with Daugavet points, Δ-points, and ∇-points.
Related
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BibTeX
@misc{langemets2026characterizing,
title = {{Characterizing the Daugavet property by squares of rank-one operators}},
author = {Johann Langemets},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.27693},
eprint = {2609.27693},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.27693},
}
RIS
TY - UNPB
TI - Characterizing the Daugavet property by squares of rank-one operators
AU - Johann Langemets
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.27693
UR - https://arxiv.org/abs/2609.27693
AB - We prove that, for real Banach spaces of dimension greater than one, each of the identities |Id+T^2|=1+|T^2| and |Id−T^2|=1+|T^2|, required for every rank-one operator T, characterizes the Daugavet property, thereby answering a question posed by Kadets, Martín, and Merí (2007). Consequently, every extremely non-complex Banach space of dimension greater than one has the Daugavet property, answering a question of Martín and Merí (2011). We also compare pointwise versions of the square Daugavet properties with Daugavet points, Δ-points, and ∇-points.
ER -