The definition of n-width of a bounded subset A in a normed linear space X is based on the existence of n-dimensional subspaces. Although the concept of an n-dimensional subspace is not available for metric trees, in this paper, using the properties of convex and compact subsets, we present a notion of n-widths for a metric tree, called Tn-widths. Later we discuss properties of Tn-widths, and s...

The aim of this paper is to motivate the development of a Brunn-Minkowski theory for minimal surfaces. In 1988, H. Rosenberg and E. Toubiana studied a sum operation for finite total curvature complete minimal surfaces in R3 and noticed that minimal hedgehogs of R3 constitute a real vector space [14]. In 1996, the author noticed that the square root of the area of minimal hedgehogs of R3 that ar...

In every dimension d ≥ 1, we establish the existence of a positive finite constant vd and of a subset Ud of R d such that the following holds: C + Ud = R d for every convex set C ⊂ R of volume at least vd and Ud contains at most log(r) r points at distance at most r from the origin, for every large r.

Let F be the finite field in q = p1 elements, £(x) be a A:-tuple of polynomials in F [xx,..., x„], V be the set of points in ¥'j satisfying F(x) = 0 and S,T be any subsets of F;. Set y)= L e{— TrU '?)) íory±Q, and 4>(K) = maxv\ 02( V)q2k. In case q = p v/e deduce from this, for example,...

In a related paper [2], the authors have shown that a homeomorphism which preserves convex sets, mapping an open subset of one locally convex topological vector space onto an open subset of another, is a projective map (the quotient of an affine operator by an affine functional). The establishment of this result in its full generality required a treatment of (possibly infinite dimensional) topo...

The minimum of quadratic functionals of the gradient on the set of convex functions ABSTRACT We study the innmum of functionals of the form R Mruru among all convex functions u 2 H 1 0 (() such that R jruj 2 = 1. (is a convex open subset of R N , and M is a given symmetric N N matrix.) We prove that this innmum is the smallest eigenvalue of M if is C 1. Otherwise the picture is more complicated...

Let K be a bounded, closed, and convex subset of a Banach space. For a Lipschitzian self-mapping A of K , we denote by Lip(A) its Lipschitz constant. In this paper, we establish a convergence property of infinite products of Lipschitzian self-mappings of K . We consider the set of all sequences {At}t=1 of such selfmappings with the property limsupt→∞ Lip(At) ≤ 1. Endowing it with an appropriate...

Let D be a nonempty compact subset of a Banach space X and denote by S(X) the family of all nonempty bounded closed convex subsets of X. We endow S(X) with the Hausdorff metric and show that there exists a set F ⊂ S(X) such that its complement S(X) \ F is σ-porous and such that for each A ∈ F and each x̃ ∈ D, the set of solutions of the best approximation problem ‖x̃− z‖ → min, z ∈ A, is nonempty...

A study is made of differentiability of the metric projection P onto a closed convex subset K of a Hubert space H. When K has nonempty interior, the Gateaux or Fréchet smoothness of its boundary can be related with some precision to Gateaux or Fréchet differentiability properties of P. For instance, combining results in §3 with earlier work of R. D. Holmes shows that K has a C2 boundary if and ...

Let G denote a connected, quasi-split reductive group over a field F that is complete with respect to a discrete valuation and that has a perfect residue field. Under mild hypotheses, we produce a subset of the Lie algebra g(F ) that picks out a G(F )-conjugacy class in every stable, regular, topologically nilpotent conjugacy class in g(F ). This generalizes an earlier result obtained by DeBack...