Rewriting Modulo βin the λΠ-Calculus Modulo

Abstract

The λ Π-calculus Modulo is a variant of the λ-calculus with dependent types where β-conversion is extended with user-defined rewrite rules. It is an expressive logical framework and has been used to encode logics and type systems in a shallow way. Basic properties such as subject reduction or uniqueness of types do not hold in general in the λ Π-calculus Modulo. However, they hold if the rewrite system generated by the rewrite rules together with β-reduction is confluent. But this is too restrictive. To handle the case where non confluence comes from the interference between the β-reduction and rewrite rules with λ-abstraction on their left-hand side, we introduce a notion of rewriting modulo β for the λ Π-calculus Modulo. We prove that confluence of rewriting modulo β is enough to ensure subject reduction and uniqueness of types. We achieve our goal by encoding the λ Π-calculus Modulo into Higher-Order Rewrite System (HRS). As a consequence, we also make the confluence results for HRSs available for the λ Π-calculus Modulo.