Atypesystemisasyntacticmethodforenforcinglevelsofabstractioninprograms.Thestudyoftypesystems--andofprogramminglanguagesfromatype-theoreticperspective--hasimportantapplicationsinsoftwareengineering,languagedesign,high-performancecompilers,andsecurity.Thistextprovidesacomprehensiveintroductio