| Preface | 6 |
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| A Guide to Closure Operations in Commutative Algebra | 12 |
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| 1 Introduction | 12 |
| 2 What Is a Closure Operation? | 13 |
| 2.1 The Basics | 13 |
| 2.2 Not-quite-closure Operations | 17 |
| 3 Constructing Closure Operations | 18 |
| 3.1 Standard Constructions | 18 |
| 3.2 Common Closures as Iterations of Standard Constructions | 20 |
| 4 Properties of Closures | 21 |
| 4.1 Star-, Semi-prime, and Prime Operations | 21 |
| 4.2 Closures Defined by Properties of (Generic) Forcing Algebras | 27 |
| 4.3 Persistence | 28 |
| 4.4 Axioms Related to the Homological Conjectures | 29 |
| 4.5 Tight Closure and Its Imitators | 31 |
| 4.6 (Homogeneous) Equational Closures and Localization | 32 |
| 5 Reductions, Special Parts of Closures, Spreads, and Cores | 33 |
| 5.1 Nakayama Closures and Reductions | 33 |
| 5.2 Special Parts of Closures | 34 |
| 6 Classes of Rings Defined by Closed Ideals | 36 |
| 6.1 When Is the Zero Ideal Closed? | 37 |
| 6.2 When Are 0 and Principal Ideals Generated by Non-zerodivisors Closed? | 37 |
| 6.3 When Are Parameter Ideals Closed (Where R Is Local)? | 38 |
| 6.4 When Is Every Ideal Closed? | 39 |
| 7 Closure Operations on (Sub)modules | 40 |
| 7.1 Torsion Theories | 42 |
| A Survey of Test Ideals | 50 |
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| 1 Introduction | 50 |
| 2 Characteristic p Preliminaries | 52 |
| 2.1 The Frobenius Endomorphism | 52 |
| 2.2 F-purity | 53 |
| 3 The Test Ideal | 55 |
| 3.1 Test Ideals of Map-pairs | 55 |
| 3.2 Test Ideals of Rings | 58 |
| 3.3 Test Ideals in Gorenstein Local Rings | 59 |
| 4 Connections with Algebraic Geometry | 61 |
| 4.1 Characteristic 0 Preliminaries | 61 |
| 4.2 Reduction to Characteristic p | 61 |
| 63 | 61 |
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| 4.3 Multiplier Ideals of Pairs | 65 |
| 4.4 Multiplier Ideals vs. Test Ideals of Divisor Pairs | 67 |
| 5 Tight Closure and Applications of Test Ideals | 68 |
| 5.1 The Briançon-Skoda Theorem | 72 |
| 5.2 Tight Closure for Modules and Test Elements | 72 |
| 6 Test Ideals for Pairs (R, at) and Applications | 74 |
| 6.1 Initial Definitions of at -test Ideals | 74 |
| 6.2 at -tight Closure | 76 |
| 6.3 Applications | 77 |
| 7 Generalizations of Pairs: Algebras of Maps | 79 |
| 8 Other Measures of Singularities in Characteristic p | 82 |
| 8.1 F-rationality | 82 |
| 8.2 F-injectivity | 83 |
| 8.3 F-signature and F-splitting Ratio | 84 |
| 8.4 Hilbert-Kunz(-Monsky) Multiplicity | 86 |
| 8.5 F-ideals, F-stable Submodules, and F-pure Centers | 89 |
| A Canonical Modules and Duality | 91 |
| A.1 Canonical Modules, Cohen-
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