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#+title: Experiments with Realizability in Univalent Type Theory | ||
#+author: Rahul Chhabra | ||
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This repository contains code for a formalisation of categorical realisability in cubical type theory. | ||
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This project is very much a work-in-progress and undergoing active hackery. As of right now, Agda will not type-check things with `--safe` enabled. | ||
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Here you can find both a timeline and an agenda of the formalisation. Some things are only formalised to the extent necessary. | ||
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* Combinatory Algebras | ||
+ [X] Applicative Structures | ||
+ [X] Feferman structure on an AS | ||
+ [X] Combinatorial completeness | ||
+ [X] Computation rule for $\lambda*$ | ||
+ Combinators | ||
+ [X] Identity, booleans, if-then-else, pairs, projections, B combinator, some Curry numerals | ||
+ [X] Computation rule for pairs | ||
+ [ ] Fixpoint combinators and primitive recursion combinator | ||
* Category of Assemblies | ||
** Definition, limits and colimits | ||
- [X] Define assemblies | ||
- [X] Define the category $\mathsf{Asm}$ | ||
- [X] Cartesian closure and similar structure | ||
- [X] Binary products | ||
- [X] Binary coproducts | ||
- [X] Equalisers | ||
- [X] Exponentials | ||
- [X] Initial and terminal objects | ||
- [X] Coequalisers | ||
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** Regular and exact | ||
- [ ] $\mathsf{Asm}$ is regular (requires Axiom of Choice) | ||
- [x] Kernel pairs of morphisms exist | ||
- [x] Kernel pairs have coequalisers | ||
- [ ] Regular epics stable under pullback | ||
- [ ] Exact completion | ||
- [x] Internal equivalence relations of a category | ||
- [ ] Functional relations | ||
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* Tripos to Topos Construction | ||
See PR #6 | ||
** A valued Predicates | ||
- [X] Heyting-valued Predicates | ||
- [X] $\forall$ and $\exists$ are adjoints | ||
- [X] Beck-Chevalley condition | ||
- [X] Heyting prealgebra structure | ||
- [X] Interpret intuitionistic logic | ||
** Realisability Topos | ||
+ [X] Partial Equivalence Relations | ||
+ [X] Functional Relations | ||
+ [X] Morphisms and RT is a category | ||
+ [X] Finite limits | ||
+ [X] Terminal object | ||
+ [X] Binary products | ||
+ [X] Equalisers (can be shown to merely exist) | ||
+ [X] Power objects | ||
+ [-] Monomorphisms | ||
+ [ ] Subobjects and pullbacks lemmas | ||
+ [ ] Power objects exist | ||
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