The minimal widths of three bounded subsets of the unit sphere associated to a unit vector in a normed linear space are studied, and three related geometric constants are introduced. New characterizations of inner product spaces are also presented. From the perspective of minimal width, strong $\varepsilon$-symmetry of Birkhoff orthogonality is introduced, and its relation to $\varepsilon$-symmetry of Birkhoff orthogonality is shown. Unlike most of the existing parameters of the underlying space, these new constants are full dimensional in nature.
Chan He
,
Horst Martini
,
Senlin Wu
. MINIMAL WIDTHS AND ORTHOGONALITY TYPES[J]. Acta mathematica scientia, Series B, 2025
, 45(1)
: 27
-39
.
DOI: 10.1007/s10473-025-0103-0
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