ABSTRACT

We present a Coq formalization of the normalization-by-evaluation algorithm for Martin-Löf dependent type theory with one universe and judgmental equality. The end results of the formalization are certified implementations of a reduction-free normalizer and of a decision procedure for term equality.

The formalization takes advantage of a graph-based variant of the Bove-Capretta method to encode mutually recursive evaluation functions with nested recursive calls. The proof of completeness, which uses the PER-model of dependent types, is formalized by relying on impredicativity of the Coq system rather than on the commonly used induction-recursion scheme which is not available in Coq. The proof of soundness is formalized by encoding logical relations as partial functions.