Definitional Extension in Type Theory

Author Tao Xue

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Tao Xue

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Tao Xue. Definitional Extension in Type Theory. In 19th International Conference on Types for Proofs and Programs (TYPES 2013). Leibniz International Proceedings in Informatics (LIPIcs), Volume 26, pp. 251-269, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)


When we extend a type system, the relation between the original system and its extension is an important issue we want to know. Conservative extension is a traditional relation we study with. But in some cases, like coercive subtyping, it is not strong enough to capture all the properties, more powerful relation between the systems is required. We bring the idea definitional extension from mathematical logic into type theory. In this paper, we study the notion of definitional extension for type theories and explicate its use, both informally and formally, in the context of coercive subtyping.
  • conservative extension
  • definitional extension
  • subtype
  • coercive subtyping


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