Robust, Semi-Intelligible Isabelle Proofs from ATP Proofs

Sledgehammer integrates external automatic theorem provers (ATPs) in the Isabelle/HOL proof assistant. To guard against bugs, ATP proofs must be reconstructed in Isabelle. Reconstructing complex proofs involves translating them to detailed Isabelle proof texts, using suitable proof methods to justify the inferences. This has been attempted before with little success, but we have addressed the main issues: Sledgehammer now transforms the proofs by contradiction into direct proofs (as described in a companion paper [4]); it reconstructs skolemization inferences; it provides the right amount of type annotations to ensure formulas are parsed correctly without overwhelming them with types; and it iteratively tests and compresses the output, resulting in simpler and faster proofs.