Animating Formal Proof at the Surface: The Jape Proof Calculator

Jape is a program which supports the step-by-step interactive development of proofs in formal logics, in the style of proofs-on-paper. It is uncommitted to any particular logic and is customized by a description of a collection of inference rules and the syntax of judgements. It works purely at the surface syntactic level, as a person working on paper might. In that spirit it makes use of explicit visible provisos rather than a conventional encoding of logical properties. Its principal mechanism is unification, employed as a search tool to defer decisions about how to proceed at difficult points in a proof. The design aim is to produce a tool which makes step-by-step proof calculations so straightforward that novices can learn by exploring the use of a pre-encoded logic. Examples of proof development are given in several small logics.