Published online by Cambridge University Press: 20 February 2018
Extending recent results by Cascales et al. [‘Plasticity of the unit ball of a strictly convex Banach space’, Rev. R. Acad. Cienc. Exactas Fís. Nat. Ser. A Mat.
110(2) (2016), 723–727], we demonstrate that for every Banach space
$X$
and every collection
$Z_{i},i\in I$
, of strictly convex Banach spaces, every nonexpansive bijection from the unit ball of
$X$
to the unit ball of the sum of
$Z_{i}$
by
$\ell _{1}$
is an isometry.
The research of the first author is supported by the Ukrainian Ministry of Science and Education Research Program 0115U000481.