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Ingram An Introduction to Inverse Limits with Set-valued Functions 123 W.T.Ingram ProfessorEmeritus DepartmentofMathematicsandStatistics MissouriUniversityofScience andTechnology 1870MinerCircle Missouri,USA ISSN2191-8198 ISSN2191-8201(electronic) ISBN978-1-4614-4486-2 ISBN978-1-4614-4487-9(eBook) DOI10.1007/978-1-4614-4487-9 SpringerNewYorkHeidelbergDordrechtLondon LibraryofCongressControlNumber:2012940256 MathematicsSubjectClassification(2010):54F15,37B45,54H20,37E05 ©W.T.Ingram2012 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof thematerialisconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation, broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionorinformation storageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilarmethodology nowknownorhereafterdeveloped.Exemptedfromthislegalreservationarebriefexcerptsinconnection with reviews or scholarly analysis or material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. 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Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) To mywife, Barbara,oursons,Billand Mark,and ourdaughter,Kathie Thisworkis alsodedicatedtothememoryof BillMahavierwho gotus startedthinking aboutinverselimitswithset-valued functions andtothememoryofmyadvisor,Howard Cook, whoseinfluenceon mycareer is immeasurable. Preface Inverselimitswithset-valuedfunctionswereintroducedin2004byBillMahavier as inverse limits with closed subsets of the unit square. In the short time since then, the subject has rapidly developed into a rich topic of research, particularly among continuum theorists. This new form of inverse limit can also show up in applicationsto economicsandin dynamicalsystems. For instance,certain models ineconomics,notablyinbackwardeconomics,caninvolvetwomappings,andthe flexibility to study the effects of using either function at each stage in the model is a valuable feature of inverse limits with set-valued functions. Recent work of BenjaminMarlinontheLorenzattractorhasprovidedevidenceofthevalueofusing set-valuedfunctionsinstudyingattractorsindynamicalsystems.Thisshortbookis notspecificallyconcernedwiththeseapplicationsofset-valuedfunctions.Instead, it is intended to provide a quick introduction to the subject of inverse limits with set-valued functions. The recently published Springer book Inverse Limits: From Continua to Chaos contains most of the background a researcher might need to makeuseoftheseinverselimitsinhisorherwork.However,ashortervolumesuch asthisonededicatedtoinverselimitswithset-valuedfunctionscouldbehelpfulto someone wanting a quick introduction to this specific subject. This short book is intendedtoprovidejustsuchanintroduction.Theemphasishereisoninverselimits ontheintervalŒ0;1(cid:2)muchasthefirstchapterofInverseLimits: FromContinuato ChaosservesasanintroductiontoinverselimitsonŒ0;1(cid:2)withmappings.Webelieve thatadeeperunderstandingofinverselimitscanbeobtainedbystudyingexamples. A major featureof this bookis the inclusion of numerousexamplesand, in many instances,modelsoftheinverselimits.Severaloftheexamplesinthisvolumehave notappearedelsewhereinprint. Major differences between the theory of inverse limits with mappings and the theory with set-valued functions arise early in this study. These differences are featured prominently in this book. However, instead of viewing these differences as a negative development, we consider them as an opportunity for further study and research. Indeed, much of the research in the subject is devoted to resolving questionsarisingfortheseveryreasons.Wehaveincludedanextensive,butbyno means exhaustive, list of currently unsolved problems in the final chapter of the book. vii viii Preface A senior-level course in analysis and, perhaps, an additional one in topology should provide a sufficient introduction to the topology of metric spaces and the topologyofproductspacestomakethematerialinthisbookaccessibletoadvanced undergraduates and, certainly, to graduate students in mathematics. An alternate sourceofbackgroundmaterialistheappendixintheSpringerbookInverseLimits: FromContinuatoChaos.Insomeoftheexamples,weassumesomefamiliaritywith inverselimitswithmappings,butnodeepunderstandingofordinaryinverselimits isnecessarytoreadthisbook. Thisbookisbasedonaseriesoflecturesgivenbytheauthorataworkshopinthe summerof2011attheInstitutodeMatema´ticas,UniversidadNacionalAuto´noma de Me´xico, in Mexico City. Many thanks go to all who participated in that short course.WeareparticularlyindebtedtoVero´nicaMart´ınezdelaVegaandAlejandro IllaneswhoorganizedtheworkshopandhelpedmakeourstayinMexicoCitysuch apleasantexperience. SpringBranch,Texas TomIngram Acknowledgments TheauthorappreciatestheassistanceofVanNall,MichelSmith,andScottVaragona whoreadsignificantportionsof the manuscript.Withouttheirproofreadingskills, therewouldhavebeenmanyadditionaltypographicalerrorsinthisbook.Theauthor remainssolelyresponsiblefortheerrorsthatremain. The authorappreciatesthe assistance and supportof everyoneat Springerwho made this volume possible. Special thanks go to Springer editor, Vaishali Damle, whoinitiallysuggestedthattheshortcourseinMexicoCitycouldserveasthebasis foraSpringerBrief. ix