关于三角范畴中由对象决定的态射的一个注记

由对象决定的态射的概念由Auslander提出.之后Krause证明了在含有Serre函子的Hom-有限的Krull-Schmidt R-线性三角范畴T中,任意态射f的决定子都存在.本文对该结论做了一个补充,给出了T中任意态射f的极小决定子D(f)的具体形式.     

φ-拓扑

§1 φ-函子在连续格理论中存在着一类具有共性的函子,如函子φ_s:范畴COM_s(对象完备格,态射保任意交)→集范畴SET,φ_(L)为L的全体单点集;φ_D:范畴COM_D(对象为完备格,态射保任意交、有向并)→SET,φ_D(L)为L的全体有向集;φ_c:范畴COM_c(对象为完备格,态射保任意交、并)→SET,φ_c(L)为L的幂集P(L)。诸如此类的函子,我们给出定义如下:     

预加法范畴中态射集星型序的刻划

本文给出了预加法范畴中态射集左（右）星序，星序的显公式刻划，证得了素性，正性预加法范畴中态射集星型序的某些刻划，把Ｈａｒｔｗｉｇ，Ｓｔｙａｎ，Ｍｉｔｒａ，Ｂａｋｓａｌａｒｙ关于复矩阵星型序刻划的有关结果推广到这两类范畴中。     

拟连续格的逆极限

给出以保任意交和定向并为态射的拟连续格范畴的逆极限,讨论函子保广义拟连续格逆极限的条件。     

态射集中的加权星序和加权广义逆

本文推广范畴上态射集中的星序理论.引进范畴上态射集中的加权星序.利用态射集的加权广义逆来刻划态射集中的加权星序.给出了态射集中的加权星序和态射的加权广义逆之间的一些关系.得到了态射集中的加权星序的一些刻划和性质.     

可数Sober空间的若干性质北大核心

可数sober空间是sober空间的一种推广.本文讨论了可数sober空间的一些性质,特别地证明了以可数sober空间为对象、以连续映射为态射的范畴CSOB为完备范畴以及从任意空间到可数sober空间的连续映射空间为可数sober空间.     

预加法范畴中态射的广义逆

该文研究预加法范畴中态射的广义逆, 利用幂等态射给出了态射广义逆存在的充要条件及其表达式. 得到预加法范畴中态射的柱心 幂零分解存在的充要条件, 并给出了分解的方法     

可数Sober空间的若干性质

可数sober空间是sober空间的一种推广.本文讨论了可数sober空间的一些性质,特别地证明了以可数sober空间为对象、以连续映射为态射的范畴CSOB为完备范畴以及从任意空间到可数sober空间的连续映射空间为可数sober空间.     

代数的局部完备集范畴和FS-局部dcpo范畴的笛卡儿闭性

本文引入了代数的局部完备集,FS-局部dcpo,局部稳定映射等概念．主要结果是：以局部Scott连续映射为态射的代数的局部完备集范畴,以局部稳定映射为态射的代数的局部完备集范畴以及以局部Scott连续映射为态射的FS-局部dcpo范畴都是笛卡儿闭范畴．     

函子范畴上加性函子的一个表示

研究函子范畴ModC上加性函子的表示,把一个Abel群作成范畴ModC上的一个左C-模,构造出一个Hom函子和一个函子态射,证明了从函子范畴ModC到范畴Ab的任意变和为积的反变左正合可加函子都与某个Hom函子自然等价.所得结论在函子范畴上,推广了Watts定理.     

The Krull-Schmidt Theorem in the Case Two

We study what happens if, in the Krull-Schmidt Theorem, instead of considering modules whose endomorphism rings have one maximal ideal, we consider modules whose endomorphism rings have two maximal ideals. If a ring has exactly two maximal right ideals, then the two maximal right ideals are necessarily two-sided. We call such a ring of type 2. The behavior of direct sums of finitely many modules whose endomorphism rings have type 2 is completely described by a graph whose connected components are either complete graphs or complete bipartite graphs. The vertices of the graphs are ideals in a suitable full subcategory of Mod-R. The edges are isomorphism classes of modules. The complete bipartite graphs give rise to a behavior described by a Weak Krull-Schmidt Theorem. Such a behavior had been previously studied for the classes of uniserial modules, biuniform modules, cyclically presented modules over a local ring, kernels of morphisms between indecomposable injective modules, and couniformly presented modules. All these modules have endomorphism rings that are either local or of type 2. Here we present a general theory that includes all these cases.     

A simplicial approach to factorization systems and Kurosh-Amitsur radicals

Regarding categories as simplicial sets via the nerve functor, we extend the notion of a factorization system from morphisms in a category, to 1-simplexes in an arbitrary simplicial set. Applied to what we call the simplicial set of short exact sequences, it gives the notion of Kurosh-Amitsur radical. That is, we present a unified approach to factorization systems and radicals.     

REDUCIBILITY IN SOME CATEGORIES OF PARTIAL RECURSIVE OPERATORS

We consider two categories with one object, namely the set of all partial functions of one variable from the set of natural numbers into itself; the morphisms are the partial recursive operators in one case, and certain continuous partial mappings in the other case. We show that these categories are recursion categories and we characterize the domains and the complete domains. Some observations are made on a notion of reducibility obtained by using the total morphisms of these categories, and, subsequently, the general recursive operators.     

Monomorphisms in the category of firm modules

Abstract

In this article, we consider the category of unitary right modules over an (associative) ring and the category of firm right modules over an idempotent ring. We study monomorphisms in these categories and give conditions under which morphisms are monomorphisms in the category of firm modules. We also prove that the lattice of categorically defined subobjects of a firm module is isomorphic to the lattice of unitary submodules of that module.     

Model Categories in Algebraic Topology

This survey of model categories and their applications in algebraic topology is intended as an introduction for non homotopy theorists, in particular category theorists and categorical topologists. We begin by defining model categories and the homotopy-like equivalence relation on their morphisms. We then explore the question of compatibility between monoidal and model structures on a category. We conclude with a presentation of the Sullivan minimal model of rational homotopy theory, including its application to the study of Lusternik–Schnirelmann category.     

Cyclically Presented Modules Over Rings of Finite Type

A ring is of finite type if it has only finitely many maximal right ideals, all two-sided. In this article, we give a complete set of invariants for finite direct sums of cyclically presented modules over a ring R of finite type. More generally, our results apply to finite direct sums of direct summands of cyclically presented right R-modules (DCP modules). Using a duality, we obtain as an application a similar set of invariants for kernels of morphisms between finite direct sums of pair-wise non-isomorphic indecomposable injective modules over an arbitrary ring. This application motivates the study of DCP modules.     

关于环上长方矩阵的加权群可逆性

研究任意环上长方矩阵的加权群逆和加权（1,5）-逆。利用矩阵分解,得到了长方矩阵积的加权群逆存在的一些等价条件和计算方法及任意环上长方矩阵的加权（1,5）-逆的刻画表达式。得到的定理推广了有关方阵群逆和（1,5）-逆的相关结果。结果还可适合应用于加法范畴中的态射。     

Krull-Schmidt decompositions for thick subcategories

Following H. Krause [Decomposing thick subcategories of the stable module category, Math. Ann. 313 (1) (1999) 95-108], we prove Krull-Schmidt type decomposition theorems for thick subcategories of various triangulated categories including the derived categories of rings, Noetherian stable homotopy categories, stable module categories over Hopf algebras, and the stable homotopy category of spectra. In all these categories, it is shown that the thick ideals of small objects decompose uniquely into indecomposable thick ideals. We also discuss some consequences of these decomposition results. In particular, it is shown that all these decompositions respect K-theory.     

Decompositions of the category of noncommutative sets and Hochschild and cyclic homology

In this note we show that the main results of the paper [PR] can be obtained as consequences of more general results concerning categories whose morphisms can be uniquely presented as compositions of morphisms of their two subcategories with the same objects. First we will prove these general results and then we will apply it to the case of finite noncommutative sets.     

Hereditary Uniserial Categories with Serre Duality

An abelian Krull-Schmidt category is said to be uniserial if the isomorphism classes of subobjects of a given indecomposable object form a linearly ordered poset. In this paper, we classify the hereditary uniserial categories with Serre duality. They fall into two types: the first type is given by the representations of the quiver A _n with linear orientation (and infinite variants thereof), the second type by tubes (and an infinite variant). These last categories give a new class of hereditary categories with Serre duality, called big tubes.