4 Algebraic Spaces

Chapter 64: Algebraic Spaces

Section 64.1: Introduction

Section 64.2: General remarks

Section 64.3: Representable morphisms of presheaves

Section 64.4: Lists of useful properties of morphisms of schemes

Section 64.5: Properties of representable morphisms of presheaves

Section 64.6: Algebraic spaces

Section 64.7: Fibre products of algebraic spaces

Section 64.8: Glueing algebraic spaces

Section 64.9: Presentations of algebraic spaces

Section 64.10: Algebraic spaces and equivalence relations

Section 64.11: Algebraic spaces, retrofitted

Section 64.12: Immersions and Zariski coverings of algebraic spaces

Section 64.13: Separation conditions on algebraic spaces

Section 64.14: Examples of algebraic spaces

Section 64.15: Change of big site

Section 64.16: Change of base scheme

Chapter 65: Properties of Algebraic Spaces

Section 65.1: Introduction

Section 65.2: Conventions

Section 65.3: Separation axioms

Section 65.4: Points of algebraic spaces

Section 65.5: Quasicompact spaces

Section 65.6: Special coverings

Section 65.7: Properties of Spaces defined by properties of schemes

Section 65.8: Constructible sets

Section 65.9: Dimension at a point

Section 65.10: Dimension of local rings

Section 65.11: Generic points

Section 65.12: Reduced spaces

Section 65.13: The schematic locus

Section 65.14: Obtaining a scheme

Section 65.15: Points on quasiseparated spaces

Section 65.16: Étale morphisms of algebraic spaces

Section 65.17: Spaces and fpqc coverings

Section 65.18: The étale site of an algebraic space

Section 65.19: Points of the small étale site

Section 65.20: Supports of abelian sheaves

Section 65.21: The structure sheaf of an algebraic space

Section 65.22: Stalks of the structure sheaf

Section 65.23: Local irreducibility

Section 65.24: Noetherian spaces

Section 65.25: Regular algebraic spaces

Section 65.26: Sheaves of modules on algebraic spaces

Section 65.27: Étale localization

Section 65.28: Recovering morphisms

Section 65.29: Quasicoherent sheaves on algebraic spaces

Section 65.30: Properties of modules

Section 65.31: Locally projective modules

Section 65.32: Quasicoherent sheaves and presentations

Section 65.33: Morphisms towards schemes

Section 65.34: Quotients by free actions

Chapter 66: Morphisms of Algebraic Spaces

Section 66.1: Introduction

Section 66.2: Conventions

Section 66.3: Properties of representable morphisms

Section 66.4: Separation axioms

Section 66.5: Surjective morphisms

Section 66.6: Open morphisms

Section 66.7: Submersive morphisms

Section 66.8: Quasicompact morphisms

Section 66.9: Universally closed morphisms

Section 66.10: Monomorphisms

Section 66.11: Pushforward of quasicoherent sheaves

Section 66.12: Immersions

Section 66.13: Closed immersions

Section 66.14: Closed immersions and quasicoherent sheaves

Section 66.15: Supports of modules

Section 66.16: Scheme theoretic image

Section 66.17: Scheme theoretic closure and density

Section 66.18: Dominant morphisms

Section 66.19: Universally injective morphisms

Section 66.20: Affine morphisms

Section 66.21: Quasiaffine morphisms

Section 66.22: Types of morphisms étale local on sourceandtarget

Section 66.23: Morphisms of finite type

Section 66.24: Points and geometric points

Section 66.25: Points of finite type

Section 66.26: Nagata spaces

Section 66.27: Quasifinite morphisms

Section 66.28: Morphisms of finite presentation

Section 66.29: Constructible sets

Section 66.30: Flat morphisms

Section 66.31: Flat modules

Section 66.32: Generic flatness

Section 66.33: Relative dimension

Section 66.34: Morphisms and dimensions of fibres

Section 66.35: The dimension formula

Section 66.36: Syntomic morphisms

Section 66.37: Smooth morphisms

Section 66.38: Unramified morphisms

Section 66.39: Étale morphisms

Section 66.40: Proper morphisms

Section 66.41: Valuative criteria

Section 66.42: Valuative criterion for universal closedness

Section 66.43: Valuative criterion of separatedness

Section 66.44: Valuative criterion of properness

Section 66.45: Integral and finite morphisms

Section 66.46: Finite locally free morphisms

Section 66.47: Rational maps

Section 66.48: Relative normalization of algebraic spaces

Section 66.49: Normalization

Section 66.50: Separated, locally quasifinite morphisms

Section 66.51: Applications

Section 66.52: Zariski's Main Theorem (representable case)

Section 66.53: Universal homeomorphisms

Chapter 67: Decent Algebraic Spaces

Section 67.1: Introduction

Section 67.2: Conventions

Section 67.3: Universally bounded fibres

Section 67.4: Finiteness conditions and points

Section 67.5: Conditions on algebraic spaces

Section 67.6: Reasonable and decent algebraic spaces

Section 67.7: Points and specializations

Section 67.8: Stratifying algebraic spaces by schemes

Section 67.9: Integral cover by a scheme

Section 67.10: Schematic locus

Section 67.11: Residue fields and henselian local rings

Section 67.12: Points on decent spaces

Section 67.13: Reduced singleton spaces

Section 67.14: Decent spaces

Section 67.15: Locally separated spaces

Section 67.16: Valuative criterion

Section 67.17: Relative conditions

Section 67.18: Points of fibres

Section 67.19: Monomorphisms

Section 67.20: Generic points

Section 67.21: Generically finite morphisms

Section 67.22: Birational morphisms

Section 67.23: Jacobson spaces

Section 67.24: Local irreducibility

Section 67.25: Catenary algebraic spaces

Chapter 68: Cohomology of Algebraic Spaces

Section 68.1: Introduction

Section 68.2: Conventions

Section 68.3: Higher direct images

Section 68.4: Finite morphisms

Section 68.5: Colimits and cohomology

Section 68.6: The alternating Čech complex

Section 68.7: Higher vanishing for quasicoherent sheaves

Section 68.8: Vanishing for higher direct images

Section 68.9: Cohomology with support in a closed subspace

Section 68.10: Vanishing above the dimension

Section 68.11: Cohomology and base change, I

Section 68.12: Coherent modules on locally Noetherian algebraic spaces

Section 68.13: Coherent sheaves on Noetherian spaces

Section 68.14: Devissage of coherent sheaves

Section 68.15: Limits of coherent modules

Section 68.16: Vanishing of cohomology

Section 68.17: Finite morphisms and affines

Section 68.18: A weak version of Chow's lemma

Section 68.19: Noetherian valuative criterion

Section 68.20: Higher direct images of coherent sheaves

Section 68.21: Ample invertible sheaves and cohomology

Section 68.22: The theorem on formal functions

Section 68.23: Applications of the theorem on formal functions

Chapter 69: Limits of Algebraic Spaces

Section 69.1: Introduction

Section 69.2: Conventions

Section 69.3: Morphisms of finite presentation

Section 69.4: Limits of algebraic spaces

Section 69.5: Descending properties

Section 69.6: Descending properties of morphisms

Section 69.7: Descending relative objects

Section 69.8: Absolute Noetherian approximation

Section 69.9: Applications

Section 69.10: Relative approximation

Section 69.11: Finite type closed in finite presentation

Section 69.12: Approximating proper morphisms

Section 69.13: Embedding into affine space

Section 69.14: Sections with support in a closed subset

Section 69.15: Characterizing affine spaces

Section 69.16: Finite cover by a scheme

Section 69.17: Obtaining schemes

Section 69.18: Glueing in closed fibres

Section 69.19: Application to modifications

Section 69.20: Universally closed morphisms

Section 69.21: Noetherian valuative criterion

Section 69.22: Refined Noetherian valuative criteria

Section 69.23: Descending finite type spaces

Chapter 70: Divisors on Algebraic Spaces

Section 70.1: Introduction

Section 70.2: Associated and weakly associated points

Section 70.3: Morphisms and weakly associated points

Section 70.4: Relative weak assassin

Section 70.5: Fitting ideals

Section 70.6: Effective Cartier divisors

Section 70.7: Effective Cartier divisors and invertible sheaves

Section 70.8: Effective Cartier divisors on Noetherian spaces

Section 70.9: Relative effective Cartier divisors

Section 70.10: Meromorphic functions and sections

Section 70.11: Relative Proj

Section 70.12: Functoriality of relative proj

Section 70.13: Invertible sheaves and morphisms into relative Proj

Section 70.14: Relatively ample sheaves

Section 70.15: Relative ampleness and cohomology

Section 70.16: Closed subspaces of relative proj

Section 70.17: Blowing up

Section 70.18: Strict transform

Section 70.19: Admissible blowups

Chapter 71: Algebraic Spaces over Fields

Section 71.1: Introduction

Section 71.2: Conventions

Section 71.3: Generically finite morphisms

Section 71.4: Integral algebraic spaces

Section 71.5: Morphisms between integral algebraic spaces

Section 71.6: Weil divisors

Section 71.7: The Weil divisor class associated to an invertible module

Section 71.8: Modifications and alterations

Section 71.9: Schematic locus

Section 71.10: Schematic locus and field extension

Section 71.11: Geometrically reduced algebraic spaces

Section 71.12: Geometrically connected algebraic spaces

Section 71.13: Geometrically irreducible algebraic spaces

Section 71.14: Geometrically integral algebraic spaces

Section 71.15: Dimension

Section 71.16: Spaces smooth over fields

Section 71.17: Euler characteristics

Section 71.18: Numerical intersections

Chapter 72: Topologies on Algebraic Spaces

Section 72.1: Introduction

Section 72.2: The general procedure

Section 72.3: Zariski topology

Section 72.4: Étale topology

Section 72.5: Smooth topology

Section 72.6: Syntomic topology

Section 72.7: Fppf topology

Section 72.8: The ph topology

Section 72.9: Fpqc topology

Chapter 73: Descent and Algebraic Spaces

Section 73.1: Introduction

Section 73.2: Conventions

Section 73.3: Descent data for quasicoherent sheaves

Section 73.4: Fpqc descent of quasicoherent sheaves

Section 73.5: Quasicoherent modules and affines

Section 73.6: Descent of finiteness properties of modules

Section 73.7: Fpqc coverings

Section 73.8: Descent of finiteness and smoothness properties of morphisms

Section 73.9: Descending properties of spaces

Section 73.10: Descending properties of morphisms

Section 73.11: Descending properties of morphisms in the fpqc topology

Section 73.12: Descending properties of morphisms in the fppf topology

Section 73.13: Application of descent of properties of morphisms

Section 73.14: Properties of morphisms local on the source

Section 73.15: Properties of morphisms local in the fpqc topology on the source

Section 73.16: Properties of morphisms local in the fppf topology on the source

Section 73.17: Properties of morphisms local in the syntomic topology on the source

Section 73.18: Properties of morphisms local in the smooth topology on the source

Section 73.19: Properties of morphisms local in the étale topology on the source

Section 73.20: Properties of morphisms smooth local on sourceandtarget

Section 73.21: Properties of morphisms étalesmooth local on sourceandtarget

Section 73.22: Descent data for spaces over spaces

Section 73.23: Descent data in terms of sheaves

Chapter 74: Derived Categories of Spaces

Section 74.1: Introduction

Section 74.2: Conventions

Section 74.3: Generalities

Section 74.4: Derived category of quasicoherent modules on the small étale site

Section 74.5: Derived category of quasicoherent modules

Section 74.6: Total direct image

Section 74.7: Being proper over a base

Section 74.8: Derived category of coherent modules

Section 74.9: Induction principle

Section 74.10: MayerVietoris

Section 74.11: The coherator

Section 74.12: The coherator for Noetherian spaces

Section 74.13: Pseudocoherent and perfect complexes

Section 74.14: Approximation by perfect complexes

Section 74.15: Generating derived categories

Section 74.16: Compact and perfect objects

Section 74.17: Derived categories as module categories

Section 74.18: Characterizing pseudocoherent complexes, I

Section 74.19: The coherator revisited

Section 74.20: Cohomology and base change, IV

Section 74.21: Cohomology and base change, V

Section 74.22: Producing perfect complexes

Section 74.23: A projection formula for Ext

Section 74.24: Limits and derived categories

Section 74.25: Cohomology and base change, VI

Section 74.26: Perfect complexes

Section 74.27: Other applications

Section 74.28: The resolution property

Section 74.29: Detecting Boundedness

Section 74.30: Quasicoherent objects in the derived category

Chapter 75: More on Morphisms of Spaces

Section 75.1: Introduction

Section 75.2: Conventions

Section 75.3: Radicial morphisms

Section 75.4: Monomorphisms

Section 75.5: Conormal sheaf of an immersion

Section 75.6: The normal cone of an immersion

Section 75.7: Sheaf of differentials of a morphism

Section 75.8: Topological invariance of the étale site

Section 75.9: Thickenings

Section 75.10: Morphisms of thickenings

Section 75.11: Picard groups of thickenings

Section 75.12: First order infinitesimal neighbourhood

Section 75.13: Formally smooth, étale, unramified transformations

Section 75.14: Formally unramified morphisms

Section 75.15: Universal first order thickenings

Section 75.16: Formally étale morphisms

Section 75.17: Infinitesimal deformations of maps

Section 75.18: Infinitesimal deformations of algebraic spaces

Section 75.19: Formally smooth morphisms

Section 75.20: Smoothness over a Noetherian base

Section 75.21: The naive cotangent complex

Section 75.22: Openness of the flat locus

Section 75.23: Critère de platitude par fibres

Section 75.24: Flatness over a Noetherian base

Section 75.25: Normalization revisited

Section 75.26: CohenMacaulay morphisms

Section 75.27: Gorenstein morphisms

Section 75.28: Slicing CohenMacaulay morphisms

Section 75.29: Reduced fibres

Section 75.30: Connected components of fibres

Section 75.31: Dimension of fibres

Section 75.32: Catenary algebraic spaces

Section 75.33: Étale localization of morphisms

Section 75.34: Zariski's Main Theorem

Section 75.35: Applications of Zariski's Main Theorem, I

Section 75.36: Stein factorization

Section 75.37: Extending properties from an open

Section 75.38: Blowing up and flatness

Section 75.39: Applications

Section 75.40: Chow's lemma

Section 75.41: Variants of Chow's Lemma

Section 75.42: Grothendieck's existence theorem

Section 75.43: Grothendieck's algebraization theorem

Section 75.44: Regular immersions

Section 75.45: Relative pseudocoherence

Section 75.46: Pseudocoherent morphisms

Section 75.47: Perfect morphisms

Section 75.48: Local complete intersection morphisms

Section 75.49: When is a morphism an isomorphism?

Section 75.50: Exact sequences of differentials and conormal sheaves

Section 75.51: Characterizing pseudocoherent complexes, II

Section 75.52: Relatively perfect objects

Section 75.53: Theorem of the cube

Section 75.54: Descent of finiteness properties of complexes

Section 75.55: Families of nodal curves

Section 75.56: The resolution property

Section 75.57: Blowing up and the resolution property

Chapter 76: Flatness on Algebraic Spaces

Section 76.1: Introduction

Section 76.2: Impurities

Section 76.3: Relatively pure modules

Section 76.4: Flat finite type modules

Section 76.5: Flat finitely presented modules

Section 76.6: A criterion for purity

Section 76.7: Flattening functors

Section 76.8: Making a map zero

Section 76.9: Flattening a map

Section 76.10: Flattening in the local case

Section 76.11: Universal flattening

Section 76.12: Grothendieck's Existence Theorem

Section 76.13: Grothendieck's Existence Theorem, bis

Chapter 77: Groupoids in Algebraic Spaces

Section 77.1: Introduction

Section 77.2: Conventions

Section 77.3: Notation

Section 77.4: Equivalence relations

Section 77.5: Group algebraic spaces

Section 77.6: Properties of group algebraic spaces

Section 77.7: Examples of group algebraic spaces

Section 77.8: Actions of group algebraic spaces

Section 77.9: Principal homogeneous spaces

Section 77.10: Equivariant quasicoherent sheaves

Section 77.11: Groupoids in algebraic spaces

Section 77.12: Quasicoherent sheaves on groupoids

Section 77.13: Colimits of quasicoherent modules

Section 77.14: Crystals in quasicoherent sheaves

Section 77.15: Groupoids and group spaces

Section 77.16: The stabilizer group algebraic space

Section 77.17: Restricting groupoids

Section 77.18: Invariant subspaces

Section 77.19: Quotient sheaves

Section 77.20: Quotient stacks

Section 77.21: Functoriality of quotient stacks

Section 77.22: The 2cartesian square of a quotient stack

Section 77.23: The 2coequalizer property of a quotient stack

Section 77.24: Explicit description of quotient stacks

Section 77.25: Restriction and quotient stacks

Section 77.26: Inertia and quotient stacks

Section 77.27: Gerbes and quotient stacks

Section 77.28: Quotient stacks and change of big site

Section 77.29: Separation conditions

Chapter 78: More on Groupoids in Spaces

Section 78.1: Introduction

Section 78.2: Notation

Section 78.3: Useful diagrams

Section 78.4: Local structure

Section 78.5: Groupoid of sections

Section 78.6: Properties of groupoids

Section 78.7: Comparing fibres

Section 78.8: Restricting groupoids

Section 78.9: Properties of groups over fields and groupoids on fields

Section 78.10: Group algebraic spaces over fields

Section 78.11: No rational curves on groups

Section 78.12: The finite part of a morphism

Section 78.13: Finite collections of arrows

Section 78.14: The finite part of a groupoid

Section 78.15: Étale localization of groupoid schemes

Chapter 79: Bootstrap

Section 79.1: Introduction

Section 79.2: Conventions

Section 79.3: Morphisms representable by algebraic spaces

Section 79.4: Properties of maps of presheaves representable by algebraic spaces

Section 79.5: Bootstrapping the diagonal

Section 79.6: Bootstrap

Section 79.7: Finding opens

Section 79.8: Slicing equivalence relations

Section 79.9: Quotient by a subgroupoid

Section 79.10: Final bootstrap

Section 79.11: Applications

Section 79.12: Algebraic spaces in the étale topology

Chapter 80: Pushouts of Algebraic Spaces

Section 80.1: Introduction

Section 80.2: Conventions

Section 80.3: Colimits of algebraic spaces

Section 80.4: Descending étale sheaves

Section 80.5: Descending étale morphisms of algebraic spaces

Section 80.6: Pushouts along thickenings and affine morphisms

Section 80.7: Pushouts along closed immersions and integral morphisms

Section 80.8: Pushouts and derived categories

Section 80.9: Constructing elementary distinguished squares

Section 80.10: Formal glueing of quasicoherent modules

Section 80.11: Formal glueing of algebraic spaces

Section 80.12: Glueing and the BeauvilleLaszlo theorem

Section 80.13: Coequalizers and glueing

Section 80.14: Compactifications