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41.
42.
43.
We show that some cardinal arithmetic configurations related to the negation of the Shelah Weak Hypothesis and natural from
the forcing point of view are impossible.
Received: 8 September 1999 / Published online: 3 October 2001 相似文献
44.
We show that for each p∈(0,1] there exists a separable p -Banach space Gp of almost universal disposition, that is, having the following extension property: for each ε>0 and each isometric embedding g:X→Y, where Y is a finite-dimensional p-Banach space and X is a subspace of Gp, there is an ε -isometry f:Y→Gp such that x=f(g(x)) for all x∈X. 相似文献
45.
We study necessary and sufficient conditions on a bounded operator T defined on the Hilbert space to be an isometry and show that, under suitable hypotheses, it suffices to restrict T to a smaller class of functions (e.g., if , to the cone of positive and decreasing functions). We also consider the problem of characterizing the sets for which the orthogonal projection of the operator T on is also an isometry. Finally, we illustrate our results with several examples involving classical operators on different settings. 相似文献
46.
M.J. de la Puente 《Linear algebra and its applications》2011,435(7):1681-1795
47.
Marion Scheepers 《Order》1990,7(1):41-64
We introduce a partition relation which is an alternate for measuring how badly the ordinary partition relation fails, we develop its corresponding partition calculus and we determine its status for various typical partially ordered sets. 相似文献
48.
Karim Johannes Becher 《manuscripta mathematica》2006,120(1):83-90
The aim of this article is to analyse a new field invariant, relevant to (formally) real fields, defined as the supremum of
the dimensions of all anisotropic, weakly isotropic quadratic forms over the field. This invariant is compared with the classical
u-invariant and with the Hasse number. Furthermore, in order to be able to obtain examples of fields where these invariants
take certain prescribed values, totally positive field extensions are studied. 相似文献
49.
The Dirichlet Laplacian in curved tubes of arbitrary cross-section rotating w.r.t. the Tang frame along infinite curves in Euclidean spaces of arbitrary dimension is investigated. If the reference curve is not straight and its curvatures vanish at infinity, we prove that the essential spectrum as a set coincides with the spectrum of the straight tube of the same cross-section and that the discrete spectrum is not empty. 相似文献
50.
Four symbolic programs, in Macsyma or Mathematica language, are presented. The first program tests forthe existence of solitons for nonlinear PDEs. It explicitly constructs solitons using Hirota's bilinear method. In the second program, the Painlevé integrability test for ODEs and PDEs is implemented. The third program provides an algorithm to compute conserved densities for nonlinear evolution equations. The fourth software package aids in the computation of Lie symmetries of systems of differential and difference-differential equations. Several examples illustrate the capabilities of the software.Research supported in part by NSF under Grant CCR-9300978. 相似文献