Formalisation of the metatheory of type theory using quotient inductive types
In this talk, I will investigate the formalisation of the metatheory of type theory in proof assistants based on intensional type theory using Agda as a vehicle. I will show how the syntax of type theory can be given as a quotient inductive inductive type (QIIT) and how this can be implemented in Agda. I argue that the QIIT-formalisation is a higher level approach than the traditional syntax (using preterms and typing relations): we can only talk about well-typed terms and every construction needs to respect the conversion relation. I will discuss how the QIIT-syntax relates to the old style syntax. I will show how models of type theory can be formalised using this approach and how parametricity and normalisation can be proved.
This is joint work with Thorsten Altenkirch and András Kovács.