Schanuel's Lemma for Exact categories

对于（非交换）群状结构的同调引理通过自对偶上下文中的图 chasing

Homological lemmas for (non-abelian) group-like structures by diagram chasing in a self-dual context

本文通过引入'诺特形式'的上下文，展示了如何在非阿贝尔群状结构范畴中，利用自对偶方法处理同调引理。

Higher extensions in exact Mal'tsev categories: distributivity of congruences and the $3^n$-Lemma

The aim of this article is to better understand the correspondence between $n$-cubic extensions and $3^n$-diagrams, which may be seen as non-abelian Yoneda extensions, useful in (co)homology of non-abelian algebraic structures. We study a higher-dimensional version of the coequaliser/kernel pair adjunction, which relates $n$-fold reflexive graphs with $n$-fold arrows in any exact Mal'tsev category. We first ask ourselves how this adjunction restricts to an equivalence of categories. This leads to the concept of an effective $n$-fold equivalence relation, corresponding to the $n$-fold regular e…

双范畴的米田引理与表示定理

Yoneda lemma and representation theorem for double categories

本文研究取值于 $\mathbb{C}\mathrm{at}$ 的正规松弛双预层，建立其米田引理、与离散双纤维化的 Grothendieck 2-等价，以及由双终对象刻画的表示定理。

Yoneda lemma for enriched infinity categories

We continue the study of enriched infinity categories, using a definition equivalent to that of Gepner and Haugseng. In our approach enriched infinity categories are associative monoids in an especially designed monoidal category of enriched quivers. We prove that, in case the monoidal structure in the basic category M comes from direct product, our definition is essentially equivalent to the approach via Segal objects. Furthermore, we compare our notion with the notion of category left-tensored over M, and prove a version of Yoneda lemma in this context. Version 2: An error in 2.6.2 corrected…

Yoneda's lemma for internal higher categories

We develop some basic concepts in the theory of higher categories internal to an arbitrary $\infty$-topos. We define internal left and right fibrations and prove a version of the Grothendieck construction and of Yoneda's lemma for internal categories.

Schur's lemma for exact categories implies abelian

We show that for a given exact category, there exists a bijection between semibricks (pairwise Hom-orthogonal set of bricks) and length wide subcategories (exact extension-closed length abelian subcategories). In particular, we show that a length exact category is abelian if and only if simple objects form a semibrick, that is, the Schur's lemma holds.

米田引理

Yoneda lemma

本文研究富集图范畴中的名称指派性质，并将米田引理推广到富集原图传输之间的连续变换上。

The Zassenhaus lemma in star-regular categories

The Noether isomorphism theorems and the Zassenhaus Lemma from group theory have a non-pointed version in a suitable categorical context first considered by W. Tholen in his PhD thesis. This article leads to a unification of these results with the ones in the pointed categorical context considered by O. Wyler, by working in the framework of star-regular categories introduced by M. Gran, Z. Janelidze and A. Ursini. Some concrete examples of categories where these results hold are examined in detail.

关键引理与普遍局部化

Key lemma and universal localization

本文研究了在任何基变换下仍保持局部化的无穷范畴局部化方法及其实现原理。

非点态语境中的同调引理

Homological Lemmas in a Non-pointed Context

本文证明经典同调引理的非点态版本在配备适当偏序单余反射子范畴的正则原模范畴中成立，并给出酉环、布尔代数、海廷代数、MV-代数及其拓扑模型和基本拓扑斯对偶范畴等实例。

Yoneda Lemma for $\mathcal{D}$-Simplicial Spaces

For a small category $\mathcal{D}$ we define fibrations of simplicial presheaves on the category $\mathcal{D}\timesΔ$, which we call localized $\mathcal{D}$-left fibration. We show these fibrations can be seen as fibrant objects in a model structure, the localized $\mathcal{D}$-covariant model structure, that is Quillen equivalent to a category of functors valued in simplicial presheaves on $\mathcal{D}$, where the Quillen equivalence is given via a generalization of the Grothendieck construction. We use our understanding of this construction to give a detailed characterization of fibrations a…

On Congruence Modular Varieties and Gumm Categories

In (B-Gran, 2004), was given a categorical formulation of the Shifting Lemma which is a characterization of the Congruence Modular Varieties among all the variety of Universal Algebra, introduced in (Gumm, 1983). Starting from a characterization of this Shifting Lemma by a property of the fibers of the fibration of points $¶\EE$ (B, 2005), on the model of what happens for Mal'tsev categories, we shall investigate three directions:\\ 1) a new one: in following the golden thread of abelian split epimorphisms naturally provided by this characterization;\\ 2) a more or less expected one: in measur…

对Eilenberg-Zilber范畴的对角引理

Diagonal Lemma for Presheaves on Eilenberg-Zilber Categories

本文研究了Eilenberg-Zilber范畴上的对角引理，证明了在Kan-Quillen模型结构下，双层简复形的逐层弱等价可诱导对角简复形的弱等价。

One-sided exact categories

One-sided exact categories appear naturally as instances of Grothendieck pretopologies. In an additive setting they are given by considering the one-sided part of Keller's axioms defining Quillen exact categories. We study one-sided exact additive categories and a stronger version defined by adding the one-sided part of Quillen "obscure axiom". We show that some homological results, such as the Short Five Lemma and the 3 X 3 Lemma, can be proved in our context. We also note that the derived category of a one-sided exact additive category can be constructed.

Enriched Yoneda Lemma

We present a version of enriched Yoneda lemma for conventional (not infinity-) categories. We require the base monoidal category to have colimits, but do not require it to be closed or symmetric monoidal.

外三角范畴中通过 $3\times 3$-引理性质的闭子函子刻画

A characterization of closed subfunctors through $3\times 3$-lemma property in extriangulated categories

本文在外三角范畴中引入子函子的3×3-引理性质，证明加法子函子闭当且仅当满足该性质，推广了Buan的结果，并给出饱和真类的新刻画。

The 3x3 lemma in the $Σ$-Maltsev and $Σ$-protomodular settings. Applications to monoids and quandles

We investigate what is remaining of the 3x3 lemma and of the denormalized 3x3 lemma, respectively valid in a pointed protomodular and in a Maltsev category, in the context of partial pointed protomodular and partial Maltsev categories, relatively to a class $Σ$ of points. The results apply, among other structures, to monoids, semirings and quandles

Facets of congruence distributivity in Goursat categories

We give new characterisations of regular Mal'tsev categories with distributive lattice of equivalence relations through variations of the so-called Triangular Lemma and Trapezoid Lemma in universal algebra. We then give new characterisations of equivalence distributive Goursat categories (which extend $3$-permutable varieties) through variations of the Triangular and Trapezoid Lemmas involving reflexive and positive relations.

Exact Categories

We survey the basics of homological algebra in exact categories in the sense of Quillen. All diagram lemmas are proved directly from the axioms, notably the five lemma, the 3 x 3-lemma and the snake lemma. We briefly discuss exact functors, idempotent completion and weak idempotent completeness. We then show that it is possible to construct the derived category of an exact category without any embedding into abelian categories and we sketch Deligne's approach to derived functors. The construction of classical derived functors with values in an abelian category painlessly translates to exact ca…

局部笛卡尔闭∞-范畴的内部约当引理

The internal Yoneda lemma for locally Cartesian closed $\infty$-categories

在有限完备、局部笛卡尔闭的∞-范畴\(\C\)中阐述并证明约当引理等的内部版本，证明仅用有限极限等，不依赖外部约当引理，并应用于初等∞-拓扑斯，恢复相关定理。

Deconstructibility and the Hill lemma in Grothendieck categories

A full subcategory of a Grothendieck category is called deconstructible if it consists of all transfinite extensions of some set of objects. This concept provides a handy framework for structure theory and construction of approximations for subcategories of Grothendieck categories. It also allows to construct model structures and t-structures on categories of complexes over a Grothendieck category. In this paper we aim to establish fundamental results on deconstructible classes and outline how to apply these in the areas mentioned above. This is related to recent work of Gillespie, Enochs, Est…

Relative homological categories

We introduce relative homological and weakly homological categories, where ``relative'' refers to a distinguished class of normal epimorphisms. It is a generalization of homological categories, but also protomodular categories can be regarded as examples. We indicate that the relative versions of various homological lemmas can be proved in a relative homological category.

Ideal cotorsion theories in triangulated categories

We study ideal cotorsion pairs associated to weak proper classes of triangles in extension closed subcategories of triangulated categories. This approach allows us to extend the recent ideal approximations theory developed by Fu, Herzog et al. for exact categories in the above mentioned context, and to provide simplified proofs for the ideal versions of some standard results as Salce's Lemma, Wakamatsu's Lemma and Christensen's Ghost Lemma. In the last part of the paper we apply the theory in order to study connections between projective classes (in particular localization or smashing subcateg…

关于truss上模范畴中正合序列的若干结果

Several results on exact sequences in categories of modules over trusses

本文在truss上模范畴中建立了蛇引理和九引理，推进了truss上模理论的范畴论研究。

Fibrations and Yoneda's lemma in an $\infty$-cosmos

We use the terms $\infty$-categories and $\infty$-functors to mean the objects and morphisms in an $\infty$-cosmos: a simplicially enriched category satisfying a few axioms, reminiscent of an enriched category of fibrant objects. Quasi-categories, Segal categories, complete Segal spaces, marked simplicial sets, iterated complete Segal spaces, $θ_n$-spaces, and fibered versions of each of these are all $\infty$-categories in this sense. Previous work in this series shows that the basic category theory of $\infty$-categories and $\infty$-functors can be developed only in reference to the axioms …

On free abelian categories for theorem proving

We give a computational approach to theorem proving in homological algebra. This approach is based on computations in the free abelian category of an additive category $\mathbf{A}$. We show that the free abelian category is amenable to explicit computations whenever we can decide homotopy equations in $\mathbf{A}$. As some consequences of our investigations, we recover Dowker's explicit formula for the connecting homomorphism $\partial$ in the snake lemma, we find a universal sense in which $\partial$ is unique, and we give a refined version of the 5-lemma.

Homology and homotopy in semi-abelian categories

The theory of abelian categories proved very useful, providing an axiomatic framework for homology and cohomology of modules over a ring and, in particular, of abelian groups. For many years, a similar categorical framework has been lacking for non-abelian (co)homology, the subject of which includes the categories of non-abelian groups, of rings, Lie algebras, etc. The notion of semi-abelian category due to Janelidze, Marki and Tholen allows a unified study of many important homological properties of such categories. For instance, in any semi-abelian category, the classical diagram lemmas (the…

范畴代数的同调视角

A Homological View of Categorical Algebra

该研究为范畴代数的同调与同伦方法构建基础，选取从z-正合范畴到阿贝尔范畴等多层公理框架并厘清其关系，开发含基本图引理的范畴计算工具，发现其可用于弱范畴环境。

Ideal approximation in $n$-exangulated categories

In this paper, we study the ideal approximation theory associated to almost $n$-exact structures in the $n$-exangulated category. The notions of $n$-ideal cotorsion pairs and $n$-$\mathbb{F}$-phantom morphisms are introduced and studied. In particular, let $\mathscr{C}$ be an extriangulated category which satisfies the condition (WIC) and $\mathcal{T}$ be a nicely embedded $n$-cluster tilting subcategory of $\mathscr{C}$, we prove Salce's Lemma in $\mathcal{T}$.

Pre-triangulated categories are triangulated

We prove a stronger version of the octahedral axiom in a pre-triangulated category. The proof uses a new lemma about exact sequences in pointed additive categories which is based on a weak converse of the snake lemma.

A bivariant Yoneda lemma and $(\infty,2)$-categories of correspondences

Everyone knows that if you have a bivariant homology theory satisfying a base change formula, you get an representation of a category of correspondences. For theories in which the covariant and contravariant transfer maps are in mutual adjunction, these data are actually equivalent. In other words, a 2-category of correspondences is the universal way to attach to a given 1-category a set of right adjoints that satisfy a base change formula. Through a bivariant version of the Yoneda paradigm, I give a definition of correspondences in higher category theory and prove an extension theorem for biv…

Exact Sequences in Non-Exact Categories (An Application to Semimodules)

We consider a notion of exact sequences in any -not necessarily exact- pointed category relative to a given (E;M)-factorization structure. We apply this notion to introduce and investigate a new notion of exact sequences of semimodules over semirings relative to the canonical image factorization. Several homological results are proved using the new notion of exactness including some restricted versions of the Short Five Lemma and the Snake Lemma opening the door for introducing and investigating homology objects in such categories. Our results apply in particular to the variety of commutative …

On the obscure axiom for one-sided exact categories

One-sided exact categories are obtained via a weakening of a Quillen exact category. Such one-sided exact categories are homologically similar to Quillen exact categories: a one-sided exact category $\mathcal{E}$ can be (essentially uniquely) embedded into its exact hull ${\mathcal{E}}^{\textrm{ex}}$; this embedding induces a derived equivalence $\textbf{D}^b(\mathcal{E}) \to \textbf{D}^b({\mathcal{E}}^{\textrm{ex}})$. Whereas it is well known that Quillen's obscure axioms are redundant for exact categories, some one-sided exact categories are known to not satisfy the corresponding obscure axi…

同调范畴中交换方块的 Lambek 不变量

Lambek Invariants of Commutative Squares in a Homological Category

本文在 Grandis 的半正合与同调范畴中研究了 Lambek 不变量，将 Lambek 同构定理推广至该范畴，并补充了相关引理的证明。

The long $n$-exact sequence theorem in $n$-abelian categories

In this note, we show that the long $n$-exact sequence theorem holds in any $n$-abelian category. As an application, the $n$-abelian version of Wakamatsu's Lemma is given.

Compact convolution

We state a Yoneda-type lemma which leads to various functor categories being compact closed.

Admissible intersection and sum property

We introduce subclasses of exact categories in terms of admissible intersections or admissible sums or both at the same time. These categories are recently studied by Brüstle, Hassoun, Shah, Tattar and Wegner to give characterisations of quasi-abelian and abelian categories. We also generalise the Schur lemma to the context of exact categories.

$\infty$-范畴的导出映射空间

Derived mapping spaces of $\infty$-categories

本文证明了导出映射空间引理，推广了 Cisinski 关于 $\infty$-范畴分数演算的核心定理，为分析范畴局部化中的映射空间提供了统一框架，并给出了立方或单纯范畴是底层范畴同伦等价局部化的充分条件。

Enriched infinity categories I: enriched presheaves

This is the first of a series of papers on enriched infinity categories, seeking to reduce enriched higher category theory to the higher algebra of presentable infinity categories, which is better understood and can be approached via universal properties. In this paper, we introduce enriched presheaves on an enriched infinity category. We prove analogues of most familiar properties of presheaves. For example, we compute limits and colimits of presheaves, prove that all presheaves are colimits of representable presheaves, and prove a version of the Yoneda lemma.

Homomorphisms of Gray-categories as pseudo algebras

Given Gray-categories $P$ and $L$, there is a Gray-category $\mathrm{Tricat}_{\mathrm{ls}}(P,L)$ of locally strict trihomomorphisms with domain $P$ and codomain $L$, tritransformations, trimodifications, and perturbations. If the domain $P$ is small and the codomain $L$ is cocomplete, we show that this Gray-category is isomorphic as a Gray-category to the Gray-category $\mathrm{Ps}$-$T$-$\mathrm{Alg}$ of pseudo algebras, pseudo functors, transformations, and modifications for a Gray-monad $T$ derived from left Kan extension. Inspired by a similar situation in two-dimensional monad theory, we a…

形式化∞-范畴米田（Yoneda）引理

Formalizing the $\infty$-Categorical Yoneda Lemma

本研究借助支持合成∞-范畴理论的新型证明助手Rzk，首次实现∞-范畴理论结论的形式化，核心成果包括范畴论基本定理米田引理的形式化，且框架内构造自动具备自然性或函子性。

一个二维范畴的蛇引理

A two-categorical Snake Lemma

本文在2-范畴中证明蛇引理，通过引入2-核、2-余核及di-正合性等概念，建立2-正合六项序列，并展示三个模型实例，推广了经典蛇引理。

Morita Theory For Derived Categories: A Bicategorical Perspective

We present a bicategorical perspective on derived Morita theory for rings, DG algebras, and spectra. This perspective draws a connection between Morita theory and the bicategorical Yoneda Lemma, yielding a conceptual unification of Morita theory in derived and bicategorical contexts. This is motivated by study of Rickard's theorem for derived equivalences of rings and of Morita theory for ring spectra, which we present in Sections 2 and 4. Along the way, we gain an understanding of the barriers to Morita theory for DG algebras and give a conceptual explanation for the counterexample of Dugger …

Exact Sequences of Semimodules over Semirings

In this paper, we introduce and investigate a new notion of exact sequences of semimodules over semirings relative to the canonical image factorization. Several homological results are proved using the new notion of exactness including some restricted versions of the Short Five Lemma and the Snake Lemma opening the door for introducing and investigating homology objects in such categories. Our results apply in particular to the variety of commutative monoids extending results in homological varieties.

Coherent Bicartesian and Sesquicartesian Categories

Coherence is here demonstrated for sesquicartesian categories, which are categories with nonempty finite products and arbitrary finite sums, including the empty sum, where moreover the first and the second projection from the product of the initial object with itself are the same. (Every bicartesian closed category, and, in particular, the category Set, is such a category.) This coherence amounts to the existence of a faithful functor from categories of this sort freely generated by sets of objects to the category of relations on finite ordinals, and it yields a very easy decision procedure fo…

你最喜欢的范畴有多原模？

How protomodular is your favourite category?

本文提出原模性的相对概念（$\mathscr{M}$-版本），分析其条件、性质（如分裂短五引理）与例子，推广了普通原模范畴。

Parametrized higher category theory and higher algebra: Exposé I -- Elements of parametrized higher category theory

We introduce the basic elements of the theory of parametrized $\infty$-categories and functors between them. These notions are defined as suitable fibrations of $\infty$-categories and functors between them. We give as many examples as we are able at this stage. Simple operations, such as the formation of opposites and the formation of functor $\infty$-categories, become slightly more involved in the parametrized setting, but we explain precisely how to perform these constructions. All of these constructions can be performed explicitly, without resorting to such acts of desperation as straight…

Applications of Exact Structures in Abelian Categories

In an abelian category $\mathscr{A}$ with small ${\rm Ext}$ groups, we show that there exists a one-to-one correspondence between any two of the following: balanced pairs, subfunctors $\mathcal{F}$ of ${\rm Ext}^{1}_{\mathscr{A}}(-,-)$ such that $\mathscr{A}$ has enough $\mathcal{F}$-projectives and enough $\mathcal{F}$-injectives and Quillen exact structures $\mathcal{E}$ with enough $\mathcal{E}$-projectives and enough $\mathcal{E}$-injectives. In this case, we get a strengthened version of the translation of the Wakamatsu lemma to the exact context, and also prove that subcategories which a…

Categorified algebra and equivariant homotopy theory

This dissertation comprises three collections of results, all united by a common theme. The theme is the study of categories via algebraic techniques, considering categories themselves as algebraic objects. This algebraic approach to category theory is central to noncommutative algebraic geometry, as realized by recent advances in the study of noncommutative motives. We have success proving algebraic results in the general setting of symmetric monoidal and semiring $\infty$-categories, which categorify abelian groups and rings, respectively. For example, we prove that modules over the semiring…

持久同调的 Quillen-McCord 定理

Persistent homological Quillen-McCord theorem

本文遵循 Barmak 的证明方案，表述并证明了关于交错距离稳定的同调 Quillen-McCord 定理，并引入持久对象、条形码式分解等工具以支撑定理的表述与应用。

Hopf braces 与半阿贝尔范畴

Hopf braces and semi-abelian categories

本文证明余交换 Hopf braces 范畴为半阿贝尔且强 protomodular，刻画其 Abel 子范畴、挠理论、局部化及中心扩张与交换子。

在双幺半范畴和拟三角Hopf代数中的余交换Hopf幺半群的原模范性

Protomodularity of cocommutative Hopf monoids in duoidal categories and quasitriangular Hopf algebras

本文将余交换Hopf代数范畴的原模范性扩展到拟三角情形，通过修改对极概念等方法，研究双幺半范畴中Hopf幺半群相关性质，证明了一些分解和引理，得到多个范畴的原模范性及相关结果，并扩展了双交叉积。