Programming Language Theory ConceptSubtypeProperties 4Hide BooksChapter 5. Types JourneyProgramming Language Theory Statusmastered Tagslanguage feature designprogramming paradigmsemanticsset theory relationtype theoryA type X that can be used wherever type Y is expected - X is \"more specific\" than Y.A type X that can be used wherever type Y is expected - X is "more specific" than Y. Previous in ConceptsSubstitution targetNext in Concepts Subtyping