Abstract. We prove that every surjective isometry between the unit spheres of two atomic JBW * -triples E and B admits a unit extension to a surjective real linear isometry from E into B. This result constitutes a new positive answer to Tignley's problem in the Jordan setting.
IntroductionIn a recent contribution we establish that every surjective isometry between the unit spheres of two B(H)-spaces extends uniquely to a surjective complex linear or conjugate linear surjective isometry between the corresponding spaces (see [15]). This result constitutes a positive answer to Tingley's isometric extension problem [31] in the setting of B(H)-spaces and atomic von Neumann algebras. Solutions to Tingley's problem for compact operators, compact C * -algebras and weakly compact JB * -triples have been previously obtained in [26,14]. For additional information on the historic background and the state of the art of Tingley's problem the reader is referred to the introduction of [15] and to the monograph [32].Problems in C * -algebras, von Neumann algebras and operator algebras are often considered in the context of Banach Jordan algebras and Jordan triple systems. Such studies widen the scope and often introduce new ideas and techniques not present in the associative case. The class of JB * -triples have a rich interaction with Banach Space Theory. The spaces in this class enjoy a unique geometry which makes more interesting the study of certain geometric problems in a wider setting. This paper is devoted to extend the recent results in [15] to the context of atomic JBW * -triples (i.e. ℓ ∞ -sums of Cartan factors).We recall that a JB * -triple is a complex Banach space E which can be equipped with a continuous triple product {., ., .} : E × E × E → E, which is symmetric and linear in the first and third variables, conjugate linear in the second variable and satisfies the following axioms , a) is an hermitian operator with non-negative spectrum; (c) L(a, a) = a 2 .2010 Mathematics Subject Classification. Primary 47B49, Secondary 46A22, 46B20, 46B04, 46A16, 46E40.