Аннотация:
We prove that if $T : X \to Y$ is a $2$-isometry between real linear $2$-normed spaces, then $T$ is affine whenever $Y$ is strictly convex. Also under some conditions we show that every surjective mapping $T : A \to B$ between real Fréchet algebras, which strongly preserves distance one, is affine.
Ключевые слова и фразы:Mazur–Ulam Theorem, Fréchet algebras, strictly convex, isometry.