Invited Papers -- Twenty Years of Theorem Proving for HOLs Past, Present and Future -- Will This Be Formal? -- Tutorials -- A Short Presentation of Coq -- An ACL2 Tutorial -- A Brief Overview of PVS -- A Brief Overview of HOL4 -- The Isabelle Framework -- Regular Papers -- A Compiled Implementation of Normalization by Evaluation -- LCF-Style Propositional Simplification with BDDs and SAT Solvers -- Nominal Inversion Principles -- Canonical Big Operators -- A Type of Partial Recursive Functions -- Formal Reasoning About Causality Analysis -- Imperative Functional Programming with Isabelle/HOL -- HOL-Boogie — An Interactive Prover for the Boogie Program-Verifier -- Secure Microkernels, State Monads and Scalable Refinement -- Certifying a Termination Criterion Based on Graphs, without Graphs -- Lightweight Separation -- Real Number Calculations and Theorem Proving -- A Formalized Theory for Verifying Stability and Convergence of Automata in PVS -- Certified Exact Transcendental Real Number Computation in Coq -- Formalizing Soundness of Contextual Effects -- First-Class Type Classes -- Formalizing a Framework for Dynamic Slicing of Program Dependence Graphs in Isabelle/HOL -- Proof Pearls -- Proof Pearl: Revisiting the Mini-rubik in Coq.