Published online by Cambridge University Press: 22 March 2023
Suppose that X and Y are two real normed spaces. A map  $f:X\rightarrow Y$ is called a min-phase-isometry if it satisfies
$f:X\rightarrow Y$ is called a min-phase-isometry if it satisfies  $$ \begin{align*} \min\{\|f(x)+f(y)\|,\|f(x)-f(y)\|\}=\min\{\|x+y\|,\|x-y\|\} \quad (x,y\in X). \end{align*} $$
$$ \begin{align*} \min\{\|f(x)+f(y)\|,\|f(x)-f(y)\|\}=\min\{\|x+y\|,\|x-y\|\} \quad (x,y\in X). \end{align*} $$
We present properties of min-phase-isometries in the case that Y is strictly convex and show that if a min-phase-isometry f (not necessarily surjective) fixes the origin, then it is phase-equivalent to a linear isometry, that is,  $f(x)=\varepsilon (x)g(x)$ for
$f(x)=\varepsilon (x)g(x)$ for  $x\in X$, where
$x\in X$, where  $g:X\rightarrow Y$ is a linear isometry and
$g:X\rightarrow Y$ is a linear isometry and  $\varepsilon $ is a map from X to
$\varepsilon $ is a map from X to  $\{-1,1\}$.
$\{-1,1\}$.
The first author is supported by the Natural Science Foundation of China (Grant No. 12271402) and the Natural Science Foundation of Tianjin City (Grant No. 22JCYBJC00420).
 ${L}_p$
-spaces
${L}_p$
-spaces 
 $\left(p>0\right)$
’, Publ. Math. Debrecen 92(3–4) (2018), 411–418.CrossRefGoogle Scholar
$\left(p>0\right)$
’, Publ. Math. Debrecen 92(3–4) (2018), 411–418.CrossRefGoogle Scholar