A half-day tutorial on Lean is scheduled as associated event of the 25th International Conference on Automated Deduction (CADE-25), which will take place in Berlin at the start of August 2015.

Lean is a new open source theorem prover being
developed at Microsoft Research, and its standard library at Carnegie
Mellon University. The *Lean* is a new theorem prover that aims to
bridge the gap between interactive and automated theorem proving, by
situating automated tools and methods in a framework that supports
user interaction and the construction of fully specified axiomatic
proofs. The goal is to support both mathematical reasoning and
reasoning about complex systems, and to verify claims in both domains.

The purpose of the tutorial is to help participants to get acquainted with Lean, and use it directly or embed it into their own systems. Participants are assumed to have only a basic grounding in logic and (functional) programming. The tutorial is divided in three parts: introduction, advanced features, and API.

In the first part, we will introduce Lean logic and language with a series of examples. Participants will be able to execute and modify all examples using any modern web browser. The course material will be based on the one used at the interactive theorem proving course at CMU.

We will also describe how to install the Lean native IDE (based on Emacs), and demonstrate basic functionality such as: continuous error checking, auto-completion, and visualization features. In the end of the first part, participants will be able to write simple definitions and prove properties about them using the web and/or native IDEs. Participants are expected to have a notebook or tablet with a Javascript enabled web-browser installed. Participants interested in the native IDE must have a Linux (Ubuntu preferred), OS X or Windows 8 notebook, and Emacs 24.x installed.

In the second part, we cover advanced features and the Lean standard library. It includes topics such as: module system, declarative proof style, type classes, implicit coercions, overloading, calculational proofs, notation declaration, and the tactic framework. The functionality will be demonstrated using fragments of the Lean standard library (e.g., category and homotopy type theory). Participants will be able to execute and modify non-trivial specifications written using Lean. Again, all the material will be available online, and participants will be able to access it before and after the tutorial.

In the final part, we cover the Lean API. This part is relevant for any participant interested in embedding Lean into their own applications and/or extending Lean. We will focus on the Lua bindings because they are easier to use than the C++ ones, and can be embedded into Lean specifications. We will demonstrate how to access Lean automation (e.g., the higher-order unification procedure, the rewriter, and decision procedures) programatically; and extend Lean with new decision procedures and tactics. Since Lua scripts can be embedded in a Lean specification, participants will be able to interactively execute and modify all examples using Leanâ€™s web IDE or native IDE.