Taclets: a new paradigm for writing theorem provers

Frameworks for interactive theorem proving give the user explicit control over the construction of proofs based on meta languages that contain dedicated control structures for describing proof construction. Such languages are not easy to master and thus contribute to the already long list of skills required by prospective users of interactive theorem provers. Most users, however, only need a convenient formalism that allows to introduce new rules with minimal overhead. On the the other hand, rules of calculi have not only purely logical content, but contain restrictions on the expected context of rule applications and heuristic information. We suggest a new and minimalist concept for implementing interactive theorem provers called taclet. Their usage can be mastered in a matter of hours, and they are efficiently compiled into the GUI of a prover. We implemented the KeY system, an interactive theorem prover for the full JavaCard language based on taclets.