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A homotopy-theoretic model of function extensionality in the effective topos

Published online by Cambridge University Press:  10 September 2018

DAN FRUMIN Open the ORCID record for DAN FRUMIN [Opens in a new window]  and
BENNO VAN DEN BERG
DAN FRUMIN
Affiliation:
Institute for Computing and Information Sciences, Radboud University, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands Email: [email protected]
BENNO VAN DEN BERG
Affiliation:
Institute for Logic, Language and Computation, Universiteit van Amsterdam, P.O. Box 94242, 1090 GE Amsterdam, The Netherlands Email: [email protected]
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Abstract

We present a way of constructing a Quillen model structure on a full subcategory of an elementary topos, starting with an interval object with connections and a certain dominance. The advantage of this method is that it does not require the underlying topos to be cocomplete. The resulting model category structure gives rise to a model of homotopy type theory with identity types, Σ- and Π-types, and functional extensionality. We apply the method to the effective topos with the interval object ∇2. In the resulting model structure we identify uniform inhabited objects as contractible objects, and show that discrete objects are fibrant. Moreover, we show that the unit of the discrete reflection is a homotopy equivalence and the homotopy category of fibrant assemblies is equivalent to the category of modest sets. We compare our work with the path object category construction on the effective topos by Jaap van Oosten.

Type
Paper
Information
Mathematical Structures in Computer Science , Volume 29 , Issue 4 , April 2019 , pp. 588 - 614
Copyright
Copyright © Cambridge University Press 2018 

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