System F with Width-subtyping and Record Updating

It is a well-known problem that F< - the polymorphic lambda calculus F extended with subtyping - does not provide so-called polymorphic updates, and that the standard PER model for F< does not provide interpretations for these operations. The polymorphic updates are interesting because they play an important role in some type-theoretic models of object-oriented languages. We present an extension Fwidth of system F with a restricted form of subtyping - width-subtyping - on record types, that does provide these operations. The main result is that we show it is still possible to give a PER model for this system.