On R-Universal Functions

We prove that the ρ-resemblance type of an R-universal function (R ≠ = ∅, ℕ) consists of one isomorphism type, but of more than one ρ-recursive isomorphism type.__________Translated from Matematicheskie Zametki, vol. 78, no. 2, 2005, pp. 259–264.Original Russian Text Copyright © 2005 by E. A. Polyakov.     

Maximal ideals of disjointness preserving operators

Let L and M be vector lattices with M Dedekind complete, and let Lr(L,M) be the vector lattice of all regular operators from L into M. We introduce the notion of maximal order ideals of disjointness preserving operators in Lr(L,M) (briefly, maximal δ-ideals of Lr(L,M)) as a generalization of the classical concept of orthomorphisms and we investigate some aspects of this ‘new’ structure. In this regard, various standard facts on orthomorphisms are extended to maximal δ-ideals. For instance, surprisingly enough, we prove that any maximal δ-ideal of Lr(L,M) is a vector lattice copy of M, when L, in addition, has an order unit. Moreover, we pay a special attention to maximal δ-ideals on continuous function spaces. As an application, we furnish a characterization of lattice bimorphisms on such spaces in terms of weigthed composition operators.     

第二特征值为(5~(0.5)-1)/2的图的结构

设G是无孤立点的简单图 ,令m(G) =max{ρ｜存在A V(G) ,G[A] Kρ}.本文给出了m(G) ≤ 3且第二特征值等于 ( 5 - 1 ) /2的图G的结构     

Antisymmetry and stability of water systems. II. Polyhedral clusters

The generalized symmetry of proton configurations of water polyhedral clusters is studied. A change in the directions of all hydrogen bonds is used as the additional approximate operation of antisymmetry. The dependence of the energy of antisymmetric configurations on the cluster stabilization energy is found. It is concluded that the internal molecular asymmetry of water that is caused by the approximate character of antisymmetry of hydrogen bonding can be of fundamental scientific importance.     

强分次环与非分次模范畴

设R是强群G-分次环,日是G的指数有限的子群.本文讨论强分次环R上一般非分次模的一些性质.首先证明一个与非分次R-模和R(H)-子模有关的Maschke-type定理,然后证明从模范畴R(H)-mod到R-mod的函子HomR(H)(R,-)与R(?)R(H)-是一对自然同构的函子以及等价条件.     

Note on a Variation of the Schröder-Bernstein Problem for Fields

In this note we study fields F with the property that the simple transcendental extension F(u) of F is isomorphic to some subfield of F but not isomorphic to F. Such a field provides one type of solution of the Schröder-Bernstein problem for fields.     

There exist non‐isomorphic STS(19) with equivalent point codes

The rows of a point by block incidence matrix of a design can be used to generate a code, the point code of the design. It is known that binary point codes of non‐isomorphic Steiner triple systems of order hr STS(v), are inequivalent when v ≤ 15, but whether this also holds for higher orders has been open. In the current paper, an example of two non‐isomorphic STS(19) with equivalent point codes is presented. © 2004 Wiley Periodicals, Inc.     

On group operations on homogeneous spaces

It is proved that every countably infinite homogeneous regular space admits a structure of any countably infinite group with continuous left shifts.

     

Approach Spaces, Limit Tower Spaces, and Probabilistic Convergence Spaces

The category LTS of limit tower spaces is defined and shown to be isomorphic to the category CAP of convergence approach spaces. The full subcategory of LTS determined by the objects satisfying a diagonal axiom due to Cook and Fischer is shown to be isomorphic to the category AP of approach spaces. A family of isomorphisms is also obtained between LTS and certain full subcategories of the category PCS of probabilistic convergence spaces.     

Computational complexity of reconstruction and isomorphism testing for designs and line graphs

Graphs with high symmetry or regularity are the main source for experimentally hard instances of the notoriously difficult graph isomorphism problem. In this paper, we study the computational complexity of isomorphism testing for line graphs of t-(v,k,λ) designs. For this class of highly regular graphs, we obtain a worst-case running time of O(vlogv+O(1)) for bounded parameters t, k, λ.In a first step, our approach makes use of the Babai-Luks algorithm to compute canonical forms of t-designs. In a second step, we show that t-designs can be reconstructed from their line graphs in polynomial-time. The first is algebraic in nature, the second purely combinatorial. For both, profound structural knowledge in design theory is required. Our results extend earlier complexity results about isomorphism testing of graphs generated from Steiner triple systems and block designs.