Categorical Models of Abadi-Plotkin's logic for parametricity

We propose a new category-theoretic formulation of relational parametricity based on a
logic for reasoning about parametricity given by Abadi and Plotkin (Plotkin and Abadi,
1993). The logic can be used to reason about parametric models, such that we may prove
consequences of parametricity that to our knowledge have not been proved before for
existing category-theoretic notions of relational parametricity. We provide examples of
parametric models and we describe a way of constructing parametric models from given
models of the second-order lambda calculus.