Boolean Systems Boolean Systems Topics in Asynchronicity Serban E. Vlad OradeaCityHalland TheSocietyofMathematicalSciencesofRomania Oradea,Romania AcademicPressisanimprintofElsevier 125LondonWall,LondonEC2Y5AS,UnitedKingdom 525BStreet,Suite1650,SanDiego,CA92101,UnitedStates 50HampshireStreet,5thFloor,Cambridge,MA02139,UnitedStates TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UnitedKingdom Copyright©2023ElsevierInc.Allrightsreserved. Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans,electronicormechanical, includingphotocopying,recording,oranyinformationstorageandretrievalsystem,withoutpermissioninwritingfromthe publisher.Detailsonhowtoseekpermission,furtherinformationaboutthePublisher’spermissionspoliciesandour arrangementswithorganizationssuchastheCopyrightClearanceCenterandtheCopyrightLicensingAgency,canbe foundatourwebsite:www.elsevier.com/permissions. 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ISBN:978-0-323-95422-8 ForinformationonallAcademicPresspublications visitourwebsiteathttps://www.elsevier.com/books-and-journals Publisher:MaraE.Conner AcquisitionsEditor:ChrisKatsaropoulos EditorialProjectManager:TomMearns ProductionProjectManager:KiruthikaGovindaraju CoverDesigner:ChristianBilbow TypesetbyVTeX ByebyeCiupi Contents Preface xix 1. Boolean functions 1 1.1. ThebinaryBoolealgebra 1 1.2. Affinespacesdefinedbytwopoints 4 1.3. Booleanfunctions 6 1.4. Duality 7 1.5. Iterates 8 1.6. Cartesianproductoffunctions 10 1.7. Successorsandpredecessors 11 1.8. FunctionsthatarecompatiblewiththeaffinestructureofBn 15 1.9. TheHammingdistance.Lipschitzfunctions 18 2. Morphisms of generator functions 21 2.1. Definition 21 2.2. Examplesofmorphisms 22 2.3. Composition 23 2.4. Isomorphisms 23 2.5. Synonymousfunctions 24 2.6. Symmetryrelativetotranslations 26 2.7. Morphismsvs.duality 26 2.8. Morphismsvs.iterates 28 2.9. Morphismsvs.Cartesianproductoffunctions 28 2.10. Morphismsvs.successorsandpredecessors 29 2.11. Morphismsvs.fixedpoints 30 vii viii Contents 3. State portraits 31 3.1. Preliminaries 31 3.2. Stateportraits 32 3.3. Stateportraitsvs.generatorfunctions 33 3.4. Examples 35 3.5. Statesubportrait 36 3.6. Isomorphisms.Duality 37 3.7. Indegree,outdegree,balancedstateportraits 38 3.8. Path,path-connectedness 39 3.9. Hamiltonianpath,Eulerianpath 40 4. Signals 41 4.1. Definition 41 4.2. Initialvalueandfinalvalue,initialtimeandfinaltime 42 4.3. Duality 42 4.4. Monotonicity 43 4.5. Orbit,orbitalequivalence 43 4.6. Omega-limitset,omega-limitequivalence 44 4.7. Theforgetfulfunction 47 4.8. Theimageofasignalviaafunction 48 4.9. Periodicity 50 5. Computation functions. Progressiveness 53 5.1. Maindefinitions 53 5.2. Morphismsofprogressivecomputationfunctions 55 5.3. Specialcasesofprogressivecomputationfunctions 57 6. Flows and equations of evolution 59 6.1. Flows 59 6.2. Reachability 62 6.3. Examples 62 Contents ix 6.4. Consistency,causalityandcomposition 64 6.5. Equationsofevolution 67 6.6. Flowswithconstantgeneratorfunctions 68 7. Systems 71 7.1. Severalequivalentperspectives 71 7.2. Definition 72 7.3. Subsystem 74 7.4. Cartesianproduct 76 8. Morphisms of flows 79 8.1. Definition 79 8.2. Inducedmorphisms 81 8.3. Morphismsofgeneratorfunctionsvs.morphismsofflows 82 8.4. Composition 83 8.5. Isomorphisms 84 8.6. Symmetryrelativetotranslations 86 8.7. Morphismscompatiblewiththesubsystems 88 8.8. Morphismsvs.duality 91 8.9. Morphismsvs.orbitsandomega-limitsets 91 8.10. Morphismsvs.Cartesianproducts 92 8.11. Morphismsvs.successorsandpredecessors 92 8.12. Morphismsvs.limits 93 8.13. Morphismsvs.orbitalandomega-limitequivalence 94 8.14. Pseudo-morphisms 95 9. Nullclines 97 9.1. Definition 97 9.2. Examples 97 9.3. Properties 99 9.4. Specialcase:NC =Bn 100 i x Contents 10. Fixed points 103 10.1. Definition 103 10.2. Fixedpointsvs.finalvalues.Restposition 104 10.3. Morphismsvs.fixedpoints 105 11. Sources, isolated fixed points, transient points, sinks 107 11.1. Definition 107 11.2. Morphisms 108 11.3. Otherproperties 109 12. Sets of reachable states 111 12.1. Convergentsequencesofsets 111 12.2. Setsofreachablestates 112 12.3. Example 115 12.4. Isomorphisms 116 13. Dependence on the initial conditions 119 13.1. Definition 119 13.2. Examples 122 13.3. Subsystem 124 13.4. Cartesianproduct 124 13.5. Isomorphisms 125 13.6. Versionsofdependenceontheinitialconditions 125 14. Periodicity 127 14.1. Eventualperiodicityanddoubleeventualperiodicity 127 14.2. Maintheorems 128 14.3. Morphismsvs.periodicity 132 14.4. Otherdefinitionsofperiodicity 133 15. Path-connectedness and topological transitivity 135 15.1. Path-connectedness 135