Generalized orderings and rings of fractions

Every total ordering of a commutative domain can be extended uniquely to its field of fractions. This result is extended in two directions. Firstly, the notion of a total ordering is generalized so that a nonzero element can have more than two signs (in fact, these signs form a group). Secondly, commutative domains are replaced by noncommutative ones and we consider the following types of rings of fractions: Ore extensions, maximal (right or two-sided) rings of fractions, division hulls of free algebras and epic fields. Throughout the paper several examples are given to illustrate the theory. Received January 8, 2005; accepted in final form November 1, 2005.     

Fresh orderings of groups

The classes of freshly and well freshly orderable groups are intro-duced, and various closure properties obtained. A short-lex ordering is a well fresh order on a free group.     

Semilinear orderings for solvable and nilpotent groups

Translated from Algebra i Logika, Vol. 29, No. 6, pp. 631–636, November–December, 1990.     

Quasi-ordered rings - A uniform approach to orderings and valuations

A quasi-order on a set S is a binary, reflexive and transitive relation on S. In [3 Fakhruddin, S. M. (1987). Quasi-ordered fields. J. Pure Appl. Algebra 45:207–210.[Crossref], [Web of Science ®] , [Google Scholar]], Fakhruddin introduced the notion of (totally) quasi-ordered fields and showed that each such field is either an ordered field or else a valued field. Hence, quasi-ordered fields are very well suited to treat ordered and valued fields simultaneously. The aim of the present paper is to prove that an analogous dichotomy holds for commutative rings with 1 as well.     

The intersection theorem for orderings of higher level in rings

This short note is ment as a supplement to the paper “On Rings admitting Orderings and 2-primary Orderings of Higher Level” by E. Becker and D. Gondard ([4]), where an intersection theorem for 2-primary orderings of higher level has been proved ([4]), Proposition 2.6). We will show that the same characterization holds for orderings of arbitrary level. This result finds several applications. For example, it is useful for the continuous representation of sums of 2n-th powers in function fields (see [8]) and it can be applied to derive several Null- and Positivstellensätze for generalized real closed fields (see [5]). As a further example we will prove a strict “Positivstellensatz of higher level” for a certain class of formally real fields. For unexplained notions we refer the reader to [4].     

Free lattice-ordered groups and the space of left orderings

For a left-orderable group G, let LO(G) denote its space of left orderings, and F(G) the free lattice-ordered group over G. This paper establishes a connection between the topology of LO(G) and the group F(G). The main result is a correspondence between the kernels of certain maps in F(G), and the closures of orbits in LO(G) under the natural G-action. The proof of this correspondence is motivated by earlier work of McCleary, which essentially shows that isolated points in LO(G) correspond to basic elements in F(G). As an application, we will study this new correspondence between kernels and the closures of orbits to show that LO(G) is either finite or uncountable. We will also show that LO(F _n ) is homeomorphic to the Cantor set, where F _n is the free group on n?>?1 generators.     

Finitely additive measures on groups and rings

On topological groups a natural finitely additive measure can be defined via compactifications. It is closely related to Hartman's concept of uniform distribution on non-compact groups (cf. [3]). Applications to several situations are possible. Some results of M. Paštéka and other authors on uniform distribution with respect to translation invariant finitely additive probability measures on Dedekind domains are transferred to more general situations. Furthermore it is shown that the range of a polynomial of degree ≥2 on a ring of algebraic integers has measure 0.     

群,环上的Fuzzy关系

一些学者已对群和环上的Ｆｕｚｚｙ关系进行了研究，本文进一步研究了群、环上的Ｆｕｚｚｙ关系，得出了若干重要的结论。     

Complete embeddings of linear orderings and embeddings of lattice-ordered groups

An infinite linearly ordered set (S,≦) is called doubly homogeneous, if its automorphism group Aut(S,≦) acts 2-transitively on it. We study embeddings of linearly ordered sets into Dedekind-completions of doubly homogeneous chains which preserve all suprema and infima, and obtain necessary and sufficient conditions for the existence of such embeddings. As one of several consequences, for each lattice-ordered groupG and each regular uncountable cardinalκ≧|G | there are 2⋉ non-isomorphic simple divisible lattice-ordered groupsH of cardinalityκ all containingG as anl-subgroup.     

Counting maximal topologies on countable groups and rings

Two non-discrete Hausdorff group topologies τ₁, τ₂ on a group G are called transversal if the least upper bound τ₁∨τ₂ of τ₁ and τ₂ is the discrete topology. We show that a countable group G admitting non-discrete Hausdorff group topologies admits c² pairwise transversal complete group topologies on G (so c² maximal group topologies). Moreover, every abelian group G admits ²|G|² pairwise transversal complete group topologies.     

PF环与群环的Grothendieck群

Let R be a commutative ring with 1, G an Abelian group, RG the group ring on R and G. In this paper we gave some properties of PF- rings in which f. g. projective modules are free. The Grothendieck groups K₀(RG) for some cases are given. In addition, for the ring R with the unimodular column property, we proved the following result: K₀(RG) ≈K₀(R), hence if R ∈PF, then K₀(RG)≈Z .     

Picard groups and infinite matrix rings

We describe a connection between the Picard group of a ring with local units and the Picard group of the unital overring . Using this connection, we show that the three groups , , and are isomorphic for any unital ring . Furthermore, each element of arises from an automorphism of , which yields an isomorphsm between and . As one application we extend a classical result of Rosenberg and Zelinsky by showing that the group is abelian for any commutative unital ring .