POPL 2026
Sun 11 - Sat 17 January 2026 Rennes, France
Tue 13 Jan 2026 11:00 - 11:22 at Belvédère - Metatheory Chair(s): Cyril Cohen

We present an intrinsic representation of type theory in the proof assistant Cubical Agda, inspired by Awodey’s natural models of type theory. The initial natural model is defined as quotient inductive-inductive-recursive types, leading us to a syntax accepted by Cubical Agda without using any transports, postulates, or custom rewrite rules. We formalise some meta-properties such as the standard model, normalisation by evaluation for typed terms, and strictification constructions. Since our formalisation is carried out using Cubical Agda’s native support for quotient inductive types, all our constructions compute at a reasonable speed. When we try to develop more sophisticated metatheory, however, the ‘transport hell’ problem reappears. Ultimately, it remains a considerable struggle to develop the metatheory of type theory using an intrinsic representation that lacks strict equations. The effort required is about the same whether or not the notion of natural model is used.

Tue 13 Jan

Displayed time zone: Brussels, Copenhagen, Madrid, Paris change

11:00 - 12:50
MetatheoryCPP at Belvédère
Chair(s): Cyril Cohen Inria, CNRS, ENS Lyon, UCBL, LIP
11:00
22m
Talk
Can we formalise type theory intrinsically without any compromise? A case study in Cubical Agda
CPP
Liang-Ting Chen Academia Sinica, Fredrik Nordvall Forsberg University of Strathclyde, Tzu-Chun Tsai Academia Sinica
DOI Pre-print
11:22
22m
Talk
Formalization of a Proof Calculus for Incremental Linearization for Satisfiability Modulo Nonlinear Arithmetic and Transcendental Functions
CPP
Tomaz Mascarenhas Universidade Federal de Minas Gerais, Harun Khan Stanford University, Abdalrhman Mohamed Stanford University, Andrew Reynolds University of Iowa, Haniel Barbosa Universidade Federal de Minas Gerais, Clark Barrett Stanford University, Cesare Tinelli University of Iowa
11:44
22m
Talk
Mechanizing Synthetic Tait Computability in Istari
CPP
Runming Li Carnegie Mellon University, Yue Yao Carnegie Mellon University, Robert Harper Carnegie Mellon University
DOI
12:06
22m
Talk
Building Blocks for Step-Indexed Program Logics
CPP
Thomas Somers Radboud University Nijmegen, Jonas Kastberg Hinrichsen Aalborg University, Lennard Gäher MPI-SWS, Robbert Krebbers Radboud University Nijmegen