On the Formal Metatheory of the Pure Type Systems using One-sorted Variable Names and Multiple Substitutions

Abstract

We develop formal theories of conversion for Church-style lambda-terms with Pi-types in first-order syntax using one-sorted variables names and Stoughton's multiple substitutions. We then formalize the Pure Type Systems along some fundamental metatheoretic properties: weakening, syntactic validity, closure under alpha-conversion and substitution. Finally, we compare our formalization with others related. The whole development has been machine-checked using the Agda system. Our work demonstrates that the mechanization of dependent type theory by using conventional syntax and without identifying alpha-convertible lambda-terms is feasible.