Journal Home Page Cumulative Index List of all Volumes Complete Contentsof this Volume Previous Article Journal of Convex Analysis 17 (2010), No. 1, 349--356Copyright Heldermann Verlag 2010 A Unified Construction Yielding Precisely Hilbert and James Sequences Spaces Dusan Repovs Faculty of Mathematics and Physics, University of Ljubljana, P. O. Box 2964, Ljubljana 1001, Slovenia dusan.repovs@guest.arnes.si Pavel V. Semenov Department of Mathematics, Moscow City Pedagogical University, 2-nd Selskokhozyastvennyi pr. 4, Moscow 129226, Russia pavels@orc.ru [Abstract-pdf] Following R. C. James' approach, we shall define the Banach space $J(e)$ for each vector $e=(e_1,e_2,...,e_d) \in \Bbb{R}^d$ with $e_1 \ne 0$. The construction immediately implies that $J(1)$ coincides with the Hilbert space $l_2$ and that $J(1;-1)$ coincides with the celebrated quasireflexive James space $J$. The results of this paper show that, up to an isomorphism, there are only these two possibilities: (i) $J(e)$ is isomorphic to $l_2$ if $e_1+e_2+...+e_d\ne 0$, and (ii) $J(e)$ is isomorphic to $J$ if $e_1+e_2+...+e_d =0$. Such a dichotomy also holds for every separable Orlicz sequence space $l_M$. Keywords: Hilbert space, Banach space, James sequence space, quasireflexive space, invertible continuous operator, Orlicz function. MSC: 54C60, 54C65, 41A65; 54C55, 54C20 [ Fulltext-pdf  (114  KB)] for subscribers only.