Inductive-Inductive Definitions

  • Fredrik Nordvall Forsberg
  • Anton Setzer
Conference paper

DOI: 10.1007/978-3-642-15205-4_35

Part of the Lecture Notes in Computer Science book series (LNCS, volume 6247)
Cite this paper as:
Nordvall Forsberg F., Setzer A. (2010) Inductive-Inductive Definitions. In: Dawar A., Veith H. (eds) Computer Science Logic. CSL 2010. Lecture Notes in Computer Science, vol 6247. Springer, Berlin, Heidelberg

Abstract

We present a principle for introducing new types in type theory which generalises strictly positive indexed inductive data types. In this new principle a set A is defined inductively simultaneously with an A-indexed set B, which is also defined inductively. Compared to indexed inductive definitions, the novelty is that the index set A is generated inductively simultaneously with B. In other words, we mutually define two inductive sets, of which one depends on the other.

Instances of this principle have previously been used in order to formalise type theory inside type theory. However the consistency of the framework used (the theorem prover Agda) is not so clear, as it allows the definition of a universe containing a code for itself. We give an axiomatisation of the new principle in such a way that the resulting type theory is consistent, which we prove by constructing a set-theoretic model.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

Copyright information

© Springer-Verlag Berlin Heidelberg 2010

Authors and Affiliations

  • Fredrik Nordvall Forsberg
    • 1
  • Anton Setzer
    • 1
  1. 1.Swansea University 

Personalised recommendations