Abstract
In this paper we show that a prototypical subtype relation that can neither be defined as a least fixed point nor as a greatest fixed point can nevertheless be defined in a dependently typed language with inductive and coinductive types. The definition proceeds alike a fold in functional programming, although a rather unusual one: that is not applied to any starting object. There has been a related construction of bisimilarity in Coq by Nakata and Uustalu recently, however, our case is not concerned with bisimilarity but a weaker notion of similarity that corresponds to recursive subtyping and has it’s own interesting problems.
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Komendantsky, V. (2012). Subtyping by Folding an Inductive Relation into a Coinductive One. In: Peña, R., Page, R. (eds) Trends in Functional Programming. TFP 2011. Lecture Notes in Computer Science, vol 7193. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-32037-8_2
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DOI: https://doi.org/10.1007/978-3-642-32037-8_2
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