extensionality

/ɪkˌstɛnʃəˈnælɪti/
noun
  1. The principle that objects or concepts are defined by their external properties or members, not by their internal descriptions; used especially in logic, mathematics, and philosophy.
    • The axiom of extensionality states that two sets are identical if they have the same elements.
    • The debate between intensionality and extensionality is central to the philosophy of language.
    • In computer science, extensionality helps define functions by their input-output behavior.
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