The simplifier in Isabelle is a very powerful tactic to discharge large classes of goals automatically. However, the results of simplifying a term not always match the user's expectation: sometimes, the resulting term is not small enough, or the simplifier even failed to apply any rule. For these cases, the simplifier offers a trace which precisely logs all steps which have been made.
These traces can be huge, especially because the library of Isabelle/HOL offers many pre-defined rewriting rules. It is often very difficult for the user to find the necessary piece of information about why and what exactly failed. Furthermore, there is no way to inspect or even influence the system while the simplification is still running. Hence, a simple, linear trace is not sufficient in these situations.
In this talk, we will present a new tracing facility which offers interactivity and a high amount of configurability. It combines successful approaches from other logic languages and adapts them to the Isabelle setup. Furthermore, it fits neatly into the Isabelle/jEdit IDE.