Sheaf theory | Homological algebra | Algebraic geometry

Injective sheaf

In mathematics, injective sheaves of abelian groups are used to construct the resolutions needed to define sheaf cohomology (and other derived functors, such as sheaf Ext). There is a further group of related concepts applied to sheaves: flabby (flasque in French), fine, soft (mou in French), acyclic. In the history of the subject they were introduced before the 1957 "Tohoku paper" of Alexander Grothendieck, which showed that the abelian category notion of injective object sufficed to found the theory. The other classes of sheaves are historically older notions. The abstract framework for defining cohomology and derived functors does not need them. However, in most concrete situations, resolutions by acyclic sheaves are often easier to construct. Acyclic sheaves therefore serve for computational purposes, for example the Leray spectral sequence. (Wikipedia).

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What is an Injective Function? Definition and Explanation

An explanation to help understand what it means for a function to be injective, also known as one-to-one. The definition of an injection leads us to some important properties of injective functions! Subscribe to see more new math videos! Music: OcularNebula - The Lopez

From playlist Functions

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Abstract Algebra | Injective Functions

We give the definition of an injective function, an outline of proving that a given function is injective, and a few examples. http://www.michael-penn.net http://www.randolphcollege.edu/mathematics/

From playlist Abstract Algebra

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The Composition of Injective(one-to-one) Functions is Injective Proof

Please Subscribe here, thank you!!! https://goo.gl/JQ8Nys Proof that the composition of injective(one-to-one) functions is also injective(one-to-one)

From playlist Proofs

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Definition of an Injective Function and Sample Proof

We define what it means for a function to be injective and do a simple proof where we show a specific function is injective. Injective functions are also called one-to-one functions. Useful Math Supplies https://amzn.to/3Y5TGcv My Recording Gear https://amzn.to/3BFvcxp (these are my affil

From playlist Injective, Surjective, and Bijective Functions

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Schemes 42: Very ample sheaves

This lecture is part of an online algebraic geometry course on schemes, based on chapter II of "Algebraic geometry" by Hartshorne. We define ample and very ample invertible sheaves for projective varieties, and gives some examples for complex elliptic curves. We also show that some sect

From playlist Algebraic geometry II: Schemes

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The Definition of an Injective(One to One) Function and Explanation

The Definition of an Injective(One to One) Function and Explanation

From playlist Functions, Sets, and Relations

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Definition of a Surjective Function and a Function that is NOT Surjective

We define what it means for a function to be surjective and explain the intuition behind the definition. We then do an example where we show a function is not surjective. Surjective functions are also called onto functions. Useful Math Supplies https://amzn.to/3Y5TGcv My Recording Gear ht

From playlist Injective, Surjective, and Bijective Functions

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Who Gives a Sheaf? Part 1: A First Example

We take a first look at (pre-)sheaves, as being inspired from first year calculus.

From playlist Who Gives a Sheaf?

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How to Prove a Function is Injective(one-to-one) Using the Definition

Please Subscribe here, thank you!!! https://goo.gl/JQ8Nys How to prove a function is injective. Injective functions are also called one-to-one functions. This is a short video focusing on the proof.

From playlist Proofs

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Schemes 3: exactness and sheaves

This lecture is part of an online algebraic geometry course on schemes, based on chapter II of "Algebraic geometry" by Hartshorne. In it we discuss exactness of morphisms of sheaves over a topological space.

From playlist Algebraic geometry II: Schemes

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Étale cohomology 9/15/2020

Čech cohomology part II, Čech-to-derived spectral sequence, Mayer-Vietoris, étale cohomology of quasi-coherent sheaves, the Artin-Schreier exact sequence and the étale cohomology of F_p in characteristic p.

From playlist Étale cohomology and the Weil conjectures

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From Cohomology to Derived Functors by Suresh Nayak

PROGRAM DUALITIES IN TOPOLOGY AND ALGEBRA (ONLINE) ORGANIZERS: Samik Basu (ISI Kolkata, India), Anita Naolekar (ISI Bangalore, India) and Rekha Santhanam (IIT Mumbai, India) DATE & TIME: 01 February 2021 to 13 February 2021 VENUE: Online Duality phenomena are ubiquitous in mathematics

From playlist Dualities in Topology and Algebra (Online)

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Schemes 4: f * and f^ 1

This lecture is part of an online algebraic geometry course on schemes, based on chapter II of "Algebraic geometry" by Hartshorne. Given a continuous map between topological spaces there are two natural ways to transfer sheaves from one space to another. We summarize the main properties of

From playlist Algebraic geometry II: Schemes

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Grothendieck-Serre Duality by Suresh Nayak

PROGRAM DUALITIES IN TOPOLOGY AND ALGEBRA (ONLINE) ORGANIZERS: Samik Basu (ISI Kolkata, India), Anita Naolekar (ISI Bangalore, India) and Rekha Santhanam (IIT Mumbai, India) DATE & TIME: 01 February 2021 to 13 February 2021 VENUE: Online Duality phenomena are ubiquitous in mathematics

From playlist Dualities in Topology and Algebra (Online)

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Schemes 27: Quasicoherent sheaves

This lecture is part of an online algebraic geometry course on schemes, based on chapter II of "Algebraic geometry" by Hartshorne. We show how to turn a module over a ring into a sheaf of modules over its spectrum. A quasicoherent sheaf of modules of one which looks locally like one constr

From playlist Algebraic geometry II: Schemes

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Charles Weibel: K-theory of line bundles and smooth varieties

The lecture was held within the framework of the Hausdorff Trimester Program: K-Theory and Related Fields. We give a K-theoretic criterion for a quasi-projective variety to be smooth, generalizing the proof of Vorst's conjecture for affine varieties. If L is a line bundle corresponding to

From playlist HIM Lectures: Trimester Program "K-Theory and Related Fields"

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Étale Cohomology - 9/24/2020

Leray spectral sequence continued, computing derived pushforwards, strict henselizations and stalks of derived pushforwards, Weil-Divisor exact sequence, cohomology of the sheaf of divisors, reduction to Galois cohomology, intro to Brauer groups

From playlist Étale cohomology and the Weil conjectures

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Schemes 45: Blowing up schemes

This lecture is part of an online algebraic geometry course on schemes, based on chapter II of "Algebraic geometry" by Hartshorne. In this lecture we discuss the operation of blowing up a scheme along a sheaf of ideals. This can be used to make ideals invertible, and to eliminate points o

From playlist Algebraic geometry II: Schemes

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Schemes 34: Coherent sheaves on projective space

This lecture is part of an online algebraic geometry course on schemes, based on chapter II of "Algebraic geometry" by Hartshorne. This lecture discusses some of Serre's theorems about coherent sheaves on projective space. In particular we describe how coherent sheaves are related to finit

From playlist Algebraic geometry II: Schemes

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Proof that if g o f is Injective(one-to-one) then f is Injective(one-to-one)

Please Subscribe here, thank you!!! https://goo.gl/JQ8Nys Proof that if g o f is Injective(one-to-one) then f is Injective(one-to-one). Given two functions f : A to B and g: B to C, we prove that if the composition g o f: A to C is an injective function then f is also an injective function

From playlist Proofs

Related pages

Injective object | Ext functor | Manifold | Projective space | Topological space | Abelian category | Leray spectral sequence | Mathematics | Sheaf cohomology | Alexander Grothendieck | Group (mathematics) | Homological algebra | Sheaf (mathematics) | Subobject classifier | Ring (mathematics) | Abelian group | Module (mathematics) | Derived functor