Tightness and Distinguished Fréchet Spaces ✩
J. Math. Anal. Appl. 324 (2006) 862–881 www.elsevier.com/locate/jmaa Tightness and distinguished Fréchet spaces ✩ J.C. Ferrando a,J.K˛akol b, M. López Pellicer c,S.A.Saxond,∗ a Centro de Investigación Operativa, Universidad M. Hernández, E-03202 Elche (Alicante), Spain b Faculty of Mathematics and Informatics, A. Mickiewicz University, 61-614 Pozna´n, Poland c Departamento de Matemática Aplicada y IMPA, Universidad Politécnica, E-46022 Valencia, Spain d Department of Mathematics, University of Florida, PO Box 11805, Gainesville, FL 32611-8105, USA Received 22 April 2005 Available online 20 January 2006 Submitted by T.D. Benavides Abstract Valdivia invented a nondistinguished Fréchet space whose weak bidual is quasi-Suslin but not K-analytic. We prove that Grothendieck/Köthe’s original nondistinguished Fréchet space serves the same purpose. In- deed, a Fréchet space is distinguished if and only if its strong dual has countable tightness, a corollary to the fact that a (DF)-space is quasibarrelled if and only if its tightness is countable. This answers a Cas- cales/Kakol/Saxon ˛ question and leads to a rich supply of (DF)-spaces whose weak duals are quasi-Suslin but not K-analytic, including the spaces Cc(κ) for κ a cardinal of uncountable cofinality. Our level of gen- erality rises above (DF)- or even dual metric spaces to Cascales/Orihuela’s class G. The small cardinals b and d invite a novel analysis of the Grothendieck/Köthe example, and are useful throughout. © 2006 Elsevier Inc. All rights reserved. Keywords: Class G; Quasibarrelled; K-analytic; Quasi-Suslin; Compact-open ✩ The research of the second author was supported by the Komitet Badan´ Naukowych (State Committee for Scientific Research), Poland, grant no.
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