Summary: Normalization by Evaluation for System F
Department of Computer Science
National Institute for Informatics
5 December 2008
Andreas Abel (LMU Munich) Normalization by Evaluation for System F NII, 2008 1 / 20
What is this for?
Theorem provers based on Curry-Howard: Coq, Agda, ...
Need to compare objects for equality.
E.g. f, g : N N. Need a proof of P(f), have one of P(g).
Extensional equality is undecidable.
Approximation: intensional equality.
Compute normal forms for f, g and compare.
The more the better: -, -, -, . . . -normal form.
NB: Coq distinguishes between P(f) and P(x. f x).
Normalization-by-evaluation excellent when is involved.
Andreas Abel (LMU Munich) Normalization by Evaluation for System F NII, 2008 2 / 20
What is Normalization By Evaluation?