A characterization of Gaussian law in Hilbert space.
A characterization of generalized inner product spaces (?-orthogonally additive mappings, III).
À la recherche de la preuve perdue: a simple proof of the Ficken theorem
A new proof of the Ficken criterion is given together with a comment concerning the known proofs and related results
A new type of orthogonality for normed planes
In this paper we introduce a new type of orthogonality for real normed planes which coincides with usual orthogonality in the Euclidean situation. With the help of this type of orthogonality we derive several characterizations of the Euclidean plane among all normed planes, all of them yielding also characteristic properties of inner product spaces among real normed linear spaces of dimensions .
A theorem on isotropic spaces
Let X be a normed space and the group of all linear surjective isometries of X that are finite-dimensional perturbations of the identity. We prove that if acts transitively on the unit sphere then X must be an inner product space.
Accretive metric projections.
Banach spaces which embed into their dual
We use Birkhoff-James' orthogonality in Banach spaces to provide new conditions for the converse of the classical Riesz representation theorem.
Characterizations of inner product spaces by strongly convex functions.
Characterizations of inner product spaces through an isosceles trapezoid property
Generalizing a property of isosceles trapezoids in the real plane into real normed spaces, a couple of characterizations of inner product spaces (i.p.s) are obtained.
Comment on ”Non-Hermitian quantum mechanics with minimal length uncertainty”.
Commuting idempotents of an -algebra.
Continuous tensor products of Hilbert spaces and product operators
Cryptohermitian picture of scattering using quasilocal metric operators.
Directionally Euclidean structures of Banach spaces
We study Banach spaces with directionally asymptotically controlled ellipsoid-approximations of the unit ball in finite-dimensional sections. Here these ellipsoids are the unique minimum volume ellipsoids, which contain the unit ball of the corresponding finite-dimensional subspace. The directional control here means that we evaluate the ellipsoids by means of a given functional of the dual space. The term 'asymptotical' refers to the fact that we take 'lim sup' over finite-dimensional subspaces. ...
Espacios de producto interno (II).
Among normal linear spaces, the inner product spaces (i.p.s.) are particularly interesting. Many characterizations of i.p.s. among linear spaces are known using various functional equations. Three functional equations characterizations of i.p.s. are based on the Frchet condition, the Jordan and von Neumann identity and the Ptolemaic inequality respectively. The object of this paper is to solve generalizations of these functional equations.
Frame functions and completeness of inner product spaces
-measures in Minkowski planes.
Interpolation functions of several matrix variables.
Jordan *-derivation pairs and quadratic functionals on modules over *-rings.
Location of the 2-centers of three points.