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math.CA2022★ 3 cited
Approximation on hexagonal domains by Taylor-Abel-Poisson means
Jürgen Prestin, Viktor Savchuk, Andrii Shidlich
Approximative properties of the Taylor-Abel-Poisson linear summation me\-thod of Fourier series are considered for functions of several variables, periodic with respect to the hexa…
math.FA2022
Decompositions in direct sum of seminormed vector spaces and Mazur-Ulam theorem
Oleksiy Dovgoshey, Jürgen Prestin, Igor Shevchuk
It was proved by S. Mazur and S. Ulam in 1932 that every isometric surjection between normed real vector spaces is affine. We generalize the Mazur--Ulam theorem and find necessary…