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math.FA2026
On the Banach-Mazur Ellipse
V. D. Babev, M. Ivanov, R. Nikolov
We provide a new proof of Ader's characterisation of the ellipse of minimal Banach-Mazur distance to the unit circle of a normed plane in terms of contact and extremal points. Our…
math.FA2025
Subdifferential determination of a primal lower regular function on a Banach space
M. Ivanov, M. Konstantinov, N. Zlateva
We generalize to Banach space Thibault-Zagrodny Theorem that if and are primal lower regular functions and locally, then and locally diffe…