OPEN PROBLEMS IN TOPOLOGY Edited by Jan van Mill Free University Amsterdam, The Netherlands George M. Reed St. Edmund Hall Oxford University Oxford, United Kingdom 1990 NORTH-HOLLAND AMSTERDAM • NEW YORK • OXFORD • TOKYO Introduction This volume grew from a discussion by the editors on the difficulty of finding good thesis problems for graduate students in topology. Although at any given time we each had our own favorite problems, we acknowledged the need to offer students a wider selection from which to choose a topic peculiar to their interests. One of us remarked, “Wouldn’t it be nice to have a book of current unsolved problems always available to pull down from the shelf?” The other replied, “Why don’t we simply produce such a book?” Two years later and not so simply, here is the resulting volume. The intent is to provide not only a source book for thesis-level problems but also a challenge to the best researchers in the field. Of course, the presented problems still reflect to some extent our own prejudices. However, as editors we have tried to represent as broad a perspective of topological research as possible. The topics range over algebraic topology, analytic set theory, continua theory, digital topology, dimension theory, domain theory, function spaces, generalized metric spaces, geometric topology, homogeneity, infinite-dimensional topology, knot theory, ordered spaces, set-theoretic topology, topological dynamics, and topological groups. Application areas include computer science, differential systems, functional analysis, and set theory. The authors are among the world leaders in their respective research areas. A key component in our specification for the volume was to provide current problems. Problems become quickly outdated, and any list soon loses its value if the status of the individual problems is uncertain. We have addressed this issue by arranging a running update on such status in each volume of the journal TOPOLOGY AND ITS APPLICATIONS. This will be useful only if the reader takes the trouble of informing one of the editors about solutions of problems posed in this book. Of course, it will also be sufficient to inform the author(s) of the paper in which the solved problem is stated. We plan a complete revision to the volume with the addition of new topics and authors within five years. To keep bookkeeping simple, each problem has two different labels. First, the label that was originally assigned to it by the author of the paper in which it is listed. The second label, the one in the outer margin, is a global one and is added by the editors; its main purpose is to draw the reader’s attention to the problems. A word on the indexes: there are two of them. The first index contains terms that are mentioned outside the problems, one may consult this index to find information on a particular subject. The second index contains terms that are mentioned in the problems, one may consult this index to locate problems concerning ones favorite subject. Although there is considerable overlap between the indexes, we think this is the best service we can offer the reader. v vi Introduction The editors would like to note that the volume has already been a success in the fact that its preparation has inspired the solution to several longoutstanding problems by the authors. We now look forward to reporting solutions by the readers. Good luck! Finally, the editors would like to thank Klaas Pieter Hart for his valuable advice on TEX and METAFONT. They also express their gratitude to Eva Coplakova for composing the indexes, and to Eva Coplakova and Geertje van Mill for typing the manuscript. Jan van Mill George M. Reed Table of Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii I Set Theoretic Topology 1 Dow’s Questions by A. Dow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steprāns’ Problems by J. Steprans . . . . . . . . . . . . . . . . 1. The Toronto Problem . . . . . . . . . . . 2. Continuous colourings of closed graphs . 3. Autohomeomorphisms of the Čech-Stone Integers . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Compactification . . . . . . . . . . . . . . . . . . . . . . . . . . on . . . . 5 . . . . . . the . . . . . 13 . 15 . 16 . 17 . 20 Tall’s Problems by F. D. Tall . . . . . . . . . . . . . . . . . . . . . . . A. Normal Moore Space Problems . . . . . . . . . . . . B. Locally Compact Normal Non-collectionwise Normal C. Collectionwise Hausdorff Problems . . . . . . . . . . D. Weak Separation Problems . . . . . . . . . . . . . . E. Screenable and Para-Lindelöf Problems . . . . . . . F. Reflection Problems . . . . . . . . . . . . . . . . . . G. Countable Chain Condition Problems . . . . . . . . H. Real Line Problems . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 23 24 25 26 28 28 30 31 32 Problems I wish I could solve by S. Watson . . . . . . . . . . . . . . . . . . . 1. Introduction . . . . . . . . . . . . . . . . . . 2. Normal not Collectionwise Hausdorff Spaces 3. Non-metrizable Normal Moore Spaces . . . . 4. Locally Compact Normal Spaces . . . . . . . 5. Countably Paracompact Spaces . . . . . . . 6. Collectionwise Hausdorff Spaces . . . . . . . 7. Para-Lindelöf Spaces . . . . . . . . . . . . . 8. Dowker Spaces . . . . . . . . . . . . . . . . . 9. Extending Ideals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 39 40 43 44 47 50 52 54 55 vii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii 10. Homeomorphisms 11. Absoluteness . . . 12. Complementation 13. Other Problems . References . . . . . . . Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 61 63 68 69 Weiss’ Questions by W. Weiss . . . . . . . . . . . . . . A. Problems about Basic Spaces . . . . B. Problems about Cardinal Invariants C. Problems about Partitions . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 79 80 81 83 Perfectly normal compacta, cosmic spaces, and some partition by G. Gruenhage . . . . . . . . . . . . . . . . . . . . . . . 1. Some Strange Questions . . . . . . . . . . . . . . . . . . 2. Perfectly Normal Compacta . . . . . . . . . . . . . . . 3. Cosmic Spaces and Coloring Axioms . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 87 89 91 94 Open Problems on βω by K. P. Hart and J. van Mill . . . . . . . 1. Introduction . . . . . . . . . . . . . . . . 2. Definitions and Notation . . . . . . . . . 3. Answers to older problems . . . . . . . . 4. Autohomeomorphisms . . . . . . . . . . . 5. Subspaces . . . . . . . . . . . . . . . . . . 6. Individual Ultrafilters . . . . . . . . . . . 7. Dynamics, Algebra and Number Theory . 8. Other . . . . . . . . . . . . . . . . . . . . 9. Uncountable Cardinals . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 99 99 100 103 105 107 109 111 118 120 On first countable, countably compact spaces III: The problem of obtaining separable noncompact examples by P. Nyikos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Topological background . . . . . . . . . . . . . . . . . . . . . . . . 2. The γN construction. . . . . . . . . . . . . . . . . . . . . . . . . . 3. The Ostaszewski-van Douwen construction. . . . . . . . . . . . . . 4. The “dominating reals” constructions. . . . . . . . . . . . . . . . . 5. Linearly ordered remainders . . . . . . . . . . . . . . . . . . . . . 6. Difficulties with manifolds . . . . . . . . . . . . . . . . . . . . . . 7. In the No Man’s Land . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 131 132 134 140 146 152 157 159 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contents ix Set-theoretic problems in Moore spaces by G. M. Reed . . . . . . . . . . . . . . . . . . . . . . 1. Introduction . . . . . . . . . . . . . . . . . . . . . . 2. Normality . . . . . . . . . . . . . . . . . . . . . . . . 3. Chain Conditions . . . . . . . . . . . . . . . . . . . 4. The collectionwise Hausdorff property . . . . . . . . 5. Embeddings and subspaces . . . . . . . . . . . . . . 6. The point-countable base problem for Moore spaces 7. Metrization . . . . . . . . . . . . . . . . . . . . . . . 8. Recent solutions . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 165 165 169 172 172 174 174 176 177 Some Conjectures by M. E. Rudin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Small Uncountable Cardinals and Topology by J. E. Vaughan. With an Appendix by S. Shelah . . . . 1. Definitions and set-theoretic problems . . . . . . . . . . . 2. Problems in topology . . . . . . . . . . . . . . . . . . . . 3. Questions raised by van Douwen in his Handbook article References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II . . . . . . . . . . . . . . . . . . . . . . . . . General Topology . . . . . 195 197 206 209 212 219 A Survey of the Class MOBI by H. R. Bennett and J. Chaber . . . . . . . . . . . . . . . . . . . . . 221 Problems on Perfect Ordered Spaces by H. R. Bennett and D. J. Lutzer . . . . . . . . . . . 1. Introduction . . . . . . . . . . . . . . . . . . . . . . 2. Perfect subspaces vs. perfect superspaces . . . . . . 3. Perfect ordered spaces and σ-discrete dense sets . . 4. How to recognize perfect generalized ordered spaces 5. A metrization problem for compact ordered spaces . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 233 233 234 235 235 236 The Point-Countable Base Problem by P. J. Collins, G. M. Reed and A. W. Roscoe 1. Origins . . . . . . . . . . . . . . . . . . . . . . 2. The point-countable base problem . . . . . . . 3. Postscript: a general structuring mechanism . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 239 242 247 249 . . . . . . . . . . . . . . . x Contents Some Open Problems in Densely Homogeneous Spaces by B. Fitzpatrick, Jr. and Zhou Hao-xuan . . . . . 1. Introduction . . . . . . . . . . . . . . . . . . . . 2. Separation Axioms . . . . . . . . . . . . . . . . . 3. The Relationship between CDH and SLH . . . . 4. Open Subsets of CDH Spaces. . . . . . . . . . . 5. Local Connectedness . . . . . . . . . . . . . . . . 6. Cartesian Products . . . . . . . . . . . . . . . . 7. Completeness . . . . . . . . . . . . . . . . . . . . 8. Modifications of the Definitions. . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 253 253 254 255 256 256 257 257 257 Large Homogeneous Compact Spaces by K. Kunen . . . . . . . . . . . 1. The Problem . . . . . . . . . . 2. Products . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 263 265 270 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Some Problems by E. Michael . . . . . . . . . . . . . . . . . . . . . 0. Introduction . . . . . . . . . . . . . . . . . . . . . 1. Inductively perfect maps, compact-covering maps, compact-covering maps . . . . . . . . . . . . . . . 2. Quotient s-maps and compact-covering maps . . . 3. Continuous selections . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . and countable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 . 273 . . . . 273 274 275 277 Questions in Dimension Theory by R. Pol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 III Continua Theory 293 Eleven Annotated Problems About Continua by H. Cook, W. T. Ingram and A. Lelek . . . . . . . . . . . . . . . . . 295 Tree-like Curves and Three Classical Problems by J. T. Rogers, Jr. . . . . . . . . . . . . . 1. The Fixed-Point Property . . . . . . . . . 2. Hereditarily Equivalent Continua . . . . . 3. Homogeneous Continua . . . . . . . . . . 4. Miscellaneous Interesting Questions . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 305 307 308 310 310 Contents IV xi Topology and Algebraic Structures 311 Problems on Topological Groups and other Homogeneous Spaces by W. W. Comfort . . . . . . . . . . . . . . . . . . . . . . . . 0. Introduction and Notation . . . . . . . . . . . . . . . . . . 1. Embedding Problems . . . . . . . . . . . . . . . . . . . . . 2. Proper Dense Subgroups . . . . . . . . . . . . . . . . . . . 3. Miscellaneous Problems . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 315 316 326 328 338 Problems in Domain Theory and Topology by J. D. Lawson and M. Mislove . . . . . . . . . . . 1. Locally compact spaces and spectral theory . . . . 2. The Scott Topology . . . . . . . . . . . . . . . . . 3. Fixed Points . . . . . . . . . . . . . . . . . . . . . 4. Function Spaces . . . . . . . . . . . . . . . . . . . 5. Cartesian Closedness . . . . . . . . . . . . . . . . 6. Strongly algebraic and finitely continuous DCPO’s 7. Dual and patch topologies . . . . . . . . . . . . . 8. Supersober and Compact Ordered Spaces . . . . . 9. Adjunctions . . . . . . . . . . . . . . . . . . . . . 10. Powerdomains . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349 352 354 357 358 360 362 364 367 368 369 370 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Topology and Computer Science Problems in the Topology of Binary Digital Images by T. Y. Kong, R. Litherland and A. Rosenfeld 1. Background . . . . . . . . . . . . . . . . . . . . 2. Two-Dimensional Thinning . . . . . . . . . . . 3. Three-Dimensional Thinning . . . . . . . . . . 4. Open Problems . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . 373 . . . . . . . On Relating Denotational and Operational Semantics Languages with Recursion and Concurrency by J.-J. Ch. Meyer and E. P. de Vink . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . Mathematical Preliminaries . . . . . . . . . . . . . . Operational Semantics . . . . . . . . . . . . . . . . . Denotational Semantics . . . . . . . . . . . . . . . . Equivalence of O and D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375 377 377 381 383 384 384 . . . . . . 387 389 390 394 396 398 for Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii Contents Conclusion and Open Problems . . . . . . . . . . . . . . . . . . . . . . . 402 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404 VI Algebraic and Geometric Topology 407 Problems on Topological Classification of Incomplete Metric by T. Dobrowolski and J. Mogilski . . . . . . . . . . . . 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 2. Absorbing sets: A Survey of Results . . . . . . . . . . 3. General Problems about Absorbing Sets . . . . . . . . 4. Problems about λ-convex Absorbing Sets . . . . . . . 5. Problems about σ-Compact Spaces . . . . . . . . . . 6. Problems about Absolute Borel Sets . . . . . . . . . . 7. Problems about Finite-Dimensional Spaces . . . . . . 8. Final Remarks . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 411 411 415 416 419 422 424 425 426 Problems about Finite-Dimensional Manifolds by R. J. Daverman . . . . . . . . . . . . . . . . . . . . . 1. Venerable Conjectures . . . . . . . . . . . . . . . . . . . 2. Manifold and Generalized Manifold Structure Problems 3. Decomposition Problems . . . . . . . . . . . . . . . . . 4. Embedding Questions . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 434 437 440 447 450 A List of Open Problems in Shape Theory by J. Dydak and J. Segal . . . . . . . . . . 1. Cohomological and shape dimensions . . 2. Movability and polyhedral shape . . . . . 3. Shape and strong shape equivalences . . 4. P -like continua and shape classifications . References . . . . . . . . . . . . . . . . . . . . Algebraic Topology by G. E. Carlsson . . . . . . . . 1. Introduction . . . . . . . . . . 2. Problem Session for Homotopy 3. H-spaces . . . . . . . . . . . . 4. K and L-theory . . . . . . . . 5. Manifolds & Bordism . . . . . 6. Transformation Groups . . . . 7. K. Pawalowski . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . Theory: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. F. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457 459 460 462 464 465 . . . . . . . . . . Adams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469 471 471 476 478 479 481 484 485
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