Chapitre II Chaînes d'idéaux d'un ensemble ordonné
Distributive ordered sets are characterized by so called generalized annihilators.
If is a class of partially ordered sets, let denote the system of all posets which are isomorphic to the system of all intervals of for some We give an algebraic characterization of elements of for being the class of all bounded posets and the class of all posets satisfying the condition that for each there exist a minimal element and a maximal element with respectively.
The concept of a 0-distributive poset is introduced. It is shown that a section semicomplemented poset is distributive if and only if it is 0-distributive. It is also proved that every pseudocomplemented poset is 0-distributive. Further, 0-distributive posets are characterized in terms of their ideal lattices.
We show that the minimum chromatic number of a product of two -chromatic graphs is either bounded by 9, or tends to infinity. The result is obtained by the study of coloring iterated adjoints of a digraph by iterated antichains of a poset.
The aim of this paper is to provide upper bounds for the entropy numbers of summation operators on trees in a critical case. In a recent paper [Studia Math. 202 (2011)] we elaborated a framework of weighted summation operators on general trees where we related the entropy of the operator to those of the underlying tree equipped with an appropriate metric. However, the results were left incomplete in a critical case of the entropy behavior, because this case requires much more involved techniques....
We investigate compactness properties of weighted summation operators as mappings from ℓ₁(T) into for some q ∈ (1,∞). Those operators are defined by , t ∈ T, where T is a tree with partial order ⪯. Here α and σ are given weights on T. We introduce a metric d on T such that compactness properties of (T,d) imply two-sided estimates for , the (dyadic) entropy numbers of . The results are applied to concrete trees, e.g. moderately increasing, biased or binary trees and to weights with α(t)σ(t)...