 The problem of full abstraction has been anticipated in a large amount of work on the relations between the denotational and operational interpretations of programming languages. In particular, the pioneering work on the semantics of recursive programs carried out in Stanford in the early 1970s by a group of people gathering around Zohar Manna, and including Jean Marie Cadiou, Robin Milner and Jean Vuillemin, also interacting with Gilles Kahn.