Dear typers, interpreting a type of a language as the set of the _values_ of the language that have that type is an idea that belongs to the type folklore. I am trying to trace back this idea, and the oldest paper I was able to find that mentions it is the Amadio and Cardelli paper on subtyping recursive types, but I am pretty sure that older references must exist. Has anyone a better (i.e. older) reference? Thanks in advance ---Beppe---