Abstract. Dependently typed programs contain an excessive amount of static terms which are necessary to please the type checker but irrelevant for computation. To obtain reasonable performance of not only the compiled program but also the type checker such static terms need to be erased as early as possible, preferably immediately after type checking. To this end, Pfenning’s type theory with irrelevant quantification, that models a distinction between static and dynamic code, is extended to universes and large eliminations. Novel is a heterogeneously typed implementation of equality which allows the smooth construction of a universal Kripke model that proves normalization, consistency and decidability.

We devise a typed equality judgement for a predicative version of Miquel’s Implicit Calculus and complete it with a calculus for explicit substitutions. The resulting theory IITT, Implicit Intensional Type Theory, is shown consistent by a partial equivalence model. We further present a bidirectional type checking and extraction algorithm and briefly sketch the integration of another notion of irrelevance, Awodey and Bauer’s bracket types. This work is aimed at providing a solid an practical foundation for extraction of efficient programs from type theory.