© 1992 by London Mathematical Society
Best Approximations in Preduals of Von Neumann Algebras
Department of Mathematics, Texas A&M University College Station, Texas 77843, USA
Department of Mathematics, University of Zurich RamiistraBe 74, CH-9001 Zurich, Switzerland
This paper characterises the semi-Chebychev subspaces of preduals of von Neumann algebras. As an application it generalises the theorem of Doob, that says that
has unique best approximations in L1(T), to a large class of preannihilators of natural non-selfadjoint operator algebras including the nest algebras. Then it studies the semi-Chebychev subspaces of the trace class operators and shows that the only Chebychev *-diagrams are triangular".
Department of Mathematics, Statistics and Computing Science, University of Texas at San Antonio, San Antonio TX, USA
Department of Mathematics, University of Texas at Austin, Austin TX, USA