Overall Objectives
Research Program
Application Domains
Highlights of the Year
New Software and Platforms
New Results
Bilateral Contracts and Grants with Industry
Partnerships and Cooperations
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Section: New Software and Platforms

TLAPS, the TLA+ Proof System

Functional Description

TLAPS, the TLA+ proof system developed at the Joint MSR-Inria Centre, is a platform for developing and mechanically verifying proofs about TLA+ specifications. The TLA+ proof language is hierarchical and explicit, allowing a user to decompose the overall proof into independent proof steps. TLAPS consists of a proof manager that interprets the proof language and generates a collection of proof obligations that are sent to backend verifiers. The current backends include the tableau-based prover Zenon for first-order logic, Isabelle/TLA+, an encoding of TLA+ as an object logic in the logical framework Isabelle, an SMT backend designed for use with any SMT-lib compatible solver, and an interface to a decision procedure for propositional temporal logic.

The current version 1.4.3 of TLAPS was released in June 2015, it is distributed under a BSD-like license. The prover fully handles the non-temporal part of TLA+. Basic temporal logic reasoning is supported through an interface with a decision procedure for propositional temporal logic that performs on-the-fly abstraction of first-order subformulas. Symmetrically, subformulas whose main operator is a connective of temporal logic are abstracted before being sent to backends for first-order logic.

A complete rewrite of the proof manager is ongoing. Its objectives are a cleaner interaction with the standard TLA+ front-ends, in particular SANY, the standard parser and semantic analyzer. This is necessary for extending the scope of the fragment of TLA+ that is handled by TLAPS, such as full temporal logic and module instantiation.

TLAPS has been used in several case studies, including the proof of determinacy of PharOS [21] and the verification of the Pastry routing protocol [22]. These case studies feed back into the development of the proof system and of its standard library.