On the extension of isometries between the unit spheres of a JBW${}^{\ast }$-triple and a Banach space

Abstract

We prove that every JBW${}^{\ast }$-triple $M$ with rank one or rank bigger than or equal to three satisfies the Mazur--Ulam property, that is, every surjective isometry from the unit sphere of $M$ onto the unit sphere of another Banach space $Y$ extends to a surjective real linear isometry from $M$ onto $Y$. We also show that the same conclusion holds if $M$ is not a JBW${}^{\ast }$-triple factor, or more generally, if the atomic part of $M^{\ast \ast }$ is not a rank two Cartan factor.