Larch Prover, or LP for short, is an interactive theorem proving system for multisorted first-order logic. It is currently used at MIT and elsewhere to reason about designs for circuits, concurrent algorithms, hardware, and software. Unlike most theorem provers, which attempt to find proofs automatically for correctly stated conjectures, LP is intended to assist users in finding and correcting flaws in conjectures---the predominant activity in the early stages of the design process.

LP works efficiently on large problems, has many important user amenities, and can be used by relatively naïve users. It was developed and is being maintained by Stephen J. Garland and John V. Guttag at the MIT Laboratory for Computer Science.