| Preface to the First Edition | 6 |
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| Preface to the Second Edition | 10 |
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| Notation | 12 |
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| Contents | 14 |
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| I Background Development | 20 |
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| 1 Semigroups and Their Ideals | 22 |
| 1.1 Semigroups | 22 |
| 1.1.1 Partial Semigroups | 28 |
| 1.2 Idempotents and Subgroups | 29 |
| 1.3 Powers of a Single Element | 32 |
| 1.4 Ideals | 33 |
| 1.5 Idempotents and Order | 37 |
| 1.6 Minimal Left Ideals | 41 |
| 1.7 Minimal Left Ideals with Idempotents | 46 |
| 1.8 Notes | 56 |
| 2 Right Topological (and Semitopological and Topological) Semigroups | 57 |
| 2.1 Topological Hierarchy | 57 |
| 2.2 Compact Right Topological Semigroups | 59 |
| 2.3 Closures and Products of Ideals | 64 |
| 2.4 Semitopological and Topological Semigroups | 67 |
| 2.5 Ellis’ Theorem | 70 |
| 2.6 Notes | 74 |
| 3 ßD -Ultrafilters and The Stone-Cech Compactification of a Discrete Space | 75 |
| 3.1 Ultrafilters | 75 |
| 3.2 The Topological Space ßD | 80 |
| 3.3 Stone–Cech Compactification | 84 |
| 3.4 More Topology of ßD | 86 |
| 3.5 Uniform Limits via Ultrafilters | 93 |
| 3.6 The Cardinality of ßD | 97 |
| 3.7 Notes | 101 |
| 3.8 Closing Remarks | 102 |
| 4 ßS – The Stone-Cech Compactification of a Discrete Semigroup | 104 |
| 4.1 Extending the Operation to ßS | 104 |
| 4.2 Commutativity in ßS | 114 |
| 4.3 S * | 116 |
| 4.4 K(ßS) and its Closure | 120 |
| 4.5 Notions of Size | 123 |
| 4.6 Notes | 125 |
| 5 ßS and Ramsey Theory – Some Easy Applications | 127 |
| 5.1 Ramsey Theory | 127 |
| 5.2 Idempotents and Finite Products | 129 |
| 5.3 Sums and Products in N | 133 |
| 5.4 Adjacent Finite Unions | 136 |
| 5.5 Compactness | 139 |
| 5.6 Notes | 141 |
| II Algebra of ßS | 144 |
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| 6 Ideals and Commutativity in ßS | 146 |
| 6.1 The Semigroup H | 146 |
| 6.2 Intersecting Left Ideals | 154 |
| 6.3 Numbers of Idempotents and Ideals – Copies of H | 156 |
| 6.4 Weakly Left Cancellative Semigroups | 169 |
| 6.5 Semiprincipal Left Ideals and the Center of p(ßS)p | 175 |
| 6.6 Principal Ideals in ßZ | 180 |
| 6.7 Ideals and Density | 183 |
| 6.8 Notes | 185 |
| 7 Groups in ßS | 187 |
| 7.1 Zelenyuk’s Theorem | 187 |
| 7.2 Semigroups Isomorphic to H | 201 |
| 7.3 Free Semigroups and Free Groups in ßS | 206 |
| 7.4 Discrete copies of Z | 211 |
| 7.5 Notes | 213 |
| 8 Cancellation | 215 |
| 8.1 Cancellation Involving Elements of S | 215 |
| 8.2 Right Cancelable Elements in ßS | 218 |
| 8.3 Right Cancellation in ßN and ßZ | 227 |
| 8.4 Left Cancelable Elements in ßS | 231 |
| 8.5 Compact Semigroups Determined by Right Cancelable Elements in Countable Groups | 236 |
| 8.6 Notes | 244 |
| 9 Idempotents | 245 |
| 9.1 Right Maximal Idempotents | 245 |
| 9.2 Topologies Defined by Idempotents | 254 |
| 9.3 Chains of Idempotents | 259 |
| 9.4 Identities in ßS | 264 |
| 9.5 Rectangular Semigroups in ßN | 265 |
| 9.6 Notes | 269 |
| 10 Homomorphisms | 271 |
| 10.1 Homomorphisms to the Circle Group | 272 |
| 10.2 Homomorphisms from ßT into S* | 276 |
| 10.3 Homomorphisms from T* into S* | 280 |
| 10.4 Isomorphisms Defined on Principal Left and Right Ideals | 285 |
| 10.5 Notes | 288 |
| 11 The Rudin–Keisler Order | 290 |
| 11.1 Connections with Right Cancelability | 291 |
| 11.2 Connections with Left Cancelability in N* | 297 |
| 11.3 Further Connections with the Algebra of ßS | 300 |
| 11.4 The Rudin-Frolík Order | 301 |
| 11.5 Notes | 303 |
| 12 Ultrafilters Generated by Finite Sums | 305 |
| 12.1 Martin’s Axiom | 305 |
| 12.2 Strongly Summable Ultrafilters – Existence | 309 |
| 12.3 Strongly Summable Ultrafilters – Independence | 315 |
| 12.4 Algebraic Properties of Strongly Summable Ultrafilters | 319 |
| 12.5 Notes | 325 |
| 13 Multiple Structures in ßS | 327 |
| 13.1 Sums Equal to Products in ßZ | 327 |
| 13.2 The Distributive Laws in ßZ | 334 |
| 13.3 Ultrafilters on R near 0 | 337 |
| 13.4 The Left and Right Continuous Extensions of One Operation | 342 |
| 13.5 Notes |
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