Theorem provers were also called 'proof checkers' because that is what they were in the beginning. They have grown powerful, however, capable in many cases to automatically produce complicated proofs. In particular, higher order logic based theorem provers such as HOL and PVS became popular because the logic is well known and very expressive. They are generally considered to be potential platforms to embed a programming logic for the purpose of formal verification. In this paper we investigate a number of most commonly used methods of embedding programming logics in such theorem provers and expose problems we discover. We will also propose an alternative approach: hybrid embedding.

m on Informatics and Mathematics. Dr Maharaj's PhD thesis was on the use of the LEGO proof system to support the Z formal notation. This work was supported by an Overseas Research Studentship from the Committee of Vice-chancellors and Principals and by the ESPRIT Basic Research Action "Types for Proofs and Programs". The thesis was supervised by Mr Anderson. Dr Maharaj has made a number of summer visits to AT&T Bell Laboratories (now known as Lucent) to work on projects involving the Higher Order Logic theorem proving system. These visits were supported by the AT&T University Relations scheme. While at Stirling, Dr Maharaj has gained experience in supervising undergraduate student projects including a project in formal methods. She has also had experience as an informal advisor to postgraduate student projects both at Stirling and at Edinburgh. Dr Maharaj is therefore ready to undertake her first experience as the official supervisor of a postgraduate student. Within Stirling, Dr M