Matthews, Seán Programming Logics, MPI for Informatics, Max Planck Society;
https://rdcu.be/dwqAI (Publisher version)
Matthews, S. (1997). Extending a Logical Framework with a Modal Connective for Validity. In M. Abadi, & T. Ito (Eds.), Theoretical Aspects of Computer Software (pp. 491-514). Berlin, Germany: Springer.