A Formal Framework with Late Binding

We deene a speciication formalism (formally, an institution) which provides a notion of dynamic type (the type which is associated to a term by a particular evaluation) and late binding (the fact that the function version to be invoked in a function application depends on the dynamic type of one or more arguments). Hence, it constitutes a natural formal framework for modeling object-oriented and other dynamically-typed languages and a basis for adding to them a speciication level. In this respect, the main novelty is the capability of writing axioms related to a given type which are not required to hold for subtypes, hence can be \overridden" in further reenements, thus lifting at the speciication level the possibility of reusing code which is ooered by the object-oriented approach.