Generic Local Structure of the Morphisms in Commutative Algebra

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310 Birger Iversen University of Aarhus, Aarhus/Danmark

Generic Local Structu re of the Morphisms in Commutative Algebra

Springer-Verlag Berlin· Heidelberg · New York 1973

AMS Subject Classifications (1970): 13-02, 14-02, 14A05, 14A 10

ISBN 3-540-06137-1 Springer-Verlag Berlin' Heidelberg· New York ISBN 0-387-06137-1 Springer-Verlag New York· Heidelberg· Berlin This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under § 54 of the German Copyright Law where copies are made for other than private use, a fee is payable to the publisher, the amount of the fee to be determined by agreement with the publisher. © by Springer-Verlag Berlin' Heidelberg 1973. Library of Congress Catalog Card Number 72-96863_

Offsetdruck: Julius Beltz, Hemsbach fBergstr.

TABLE OF CONTENTS INTRODUCTION LEITFADEN Chapter I

3 UNRAMIFIED MORPHISMS

I.j

Derivations and differentials

4

1.2

Unramified morphisms

7

1.3

Jnramified algebras over a field

11

1.4

Cartier's equality

13

1.5

Separable field extensions

15

1.6

~

1.7

TI

1.8

Geometrically irreducible algebras

21

1,9

Irreducible components and base extension

24

I.C

Multiplicative coa

26

Chapter II

18

and separability o

of algebras over a field

ebras

19

SMOOTH MORPHISMS

II.J

Smooth functors

33

11.2

Infinitesimal extensions

36

11.3

The (truncated) cotangent complex

37

11.4

Jacobian criterion for smoothness

39

11.5

Cohen's theorem

42

11.6

Smooth localities over a field

43

11.7

Dimension formulas

46

11.8

Special criterionsfor smooth localities

48

(Cartier's theorem)

II. II.

Appendix F.

Relative finitene s conditions

49

Appendix T.

Tangent spaces

52

IV Chapte~

III

ETALE MORPHISMS

111.1

Etale morphisms

63

111.2

Local structure theorem

63

111.3

Applications to smooth

111.4

Grothendieck Hensel Lemma

66

111.5

Henselian local rings

67

111.6

Henselization of a local ring

71

111.7

Newton's method

71

111.8

Etale algebras over a local.

111.9

Local

~amification

65

mo~phisms

no~mal

domain

79

theory

111.10 Ramification theory for normal domains [LB.f. :L

III.R

Chapter IV

:L

=

74 130

n)

Topology on rational points

83

SOME fUNDAMENTAL THEOREMS 90

Nullstellensatz

IV.1

Hilbe~t's

IV.2 IV.3 IV.C

Zariski's main theorem Chevalley's constructibility The analytic case

93 theo~em

96

99

BIBLIOGRAPHY

103

INDEX OF NOTATIONS

106

INDEX OF SYMBOLS

108

INTRODUCTION These notes treat in the framework of commutative algebra the structure of the morphisms between algebraic varieties. The corresponding notion in differential geometry is Coo-maps

for which the tangent maps T (f)

has maximal rank. There are obviously three possibilities j)

T (fJ

injective

2)

T (fJ x T (f)

surjective

3)

x

x

x

bijective

The corresponding notions in commutative algebra are j)

unrami