Theorem Proving in Higher Order Logics

This volume constitutes the proceedings of the 21st International Conference on Theorem Proving in Higher Order Logics (TPHOLs 2008), which was held during August 18 21, 2008 in Montreal, Canada. TPHOLs covers all aspects of theorem proving in higher order logics as well as related topics in theorem proving and veri?cation. There were 40 papers submitted to TPHOLs 2008 in the full research c- egory, each of which was refereed by at least four reviewers selected by the ProgramCommittee. Of these submissions, 17 researchpapers and 1 proofpearl were accepted for presentation at the conference and publication in this v- ume. In keeping with longstanding tradition, TPHOLs 2008 also o?ered a venue for the presentation of emerging trends, where researchers invited discussion by means of a brief introductory talk and then discussed their work at a poster session. A supplementary proceedings volume was published as a 2008 technical report of Concordia University. The organizersaregratefulto MichaelGordonand StevenMiller for agreeing togiveinvitedtalksatTPHOLs2008.Aspartofthecelebrationofthe20yearsof TPHOLs, TPHOLs 2008 invited tool developers and expert users to give special tool presentations of the most representative theorem provers in higher order logics. The following speakers kindly accepted our invitation and we aregrateful tothem:YvesBertot(Coq),MattKaufmann(ACL2),SamOwre(PVS),Konrad Slind (HOL), and Makarius Wenzel (Isabelle).