System Description: Abella -- A System for Reasoning about Computations

Abella [Gac08] is an interactive theorem prover for reasoning about the properties of an object language that is described through structural operational semantics style rules. Abella is based on a two-level logic approach to specification and reasoning. One level is defined by a specification logic which supports a transparent encoding of structural operational semantics rules and also enables their execution. The second level, called the reasoning logic, embeds the specification logic and allows the development of proofs of properties about specifications. An important characteristic of both logics is that they exploit the λ-tree syntax approach to treating binding in object language constructs. Amongst other things, Abella has been used to prove normalizability properties of the λ-calculus, cut-admissibility for a sequent calculus and type uniqueness and subject reduction properties. This paper briefly discusses the logical foundations of Abella, outlines the style of theorem proving that it supports and finally describes some of its recent applications.