Alt-Ergo Explained

Alt-Ergo
Developer:	OCamlPro
Programming Language:	OCaml
Language:	English
Genre:	Mathematical solver, program verifier

Alt-Ergo, an automatic solver for mathematical formulas, is mainly used in formal program verification. It operates on the principle of satisfiability modulo theories (SMT). Development was undertaken by researchers at the Paris-Sud University, Laboratoire de Recherche en Informatique, Inria Saclay Ile-de-France, and CNRS. Since 2013, project management and oversight has been conducted by OCamlPro company.^[1] It is released under the free and open-source software CeCILL-C license.

Technologies

Design choices

Alt-Ergo employs a specialized input language with prenex polymorphism, designed to reduce the number of axioms requiring quantification and to simplify the complexity of problems. While Alt-Ergo offers partial support for the SMT-LIB 2 language, its efficiency with SMT files is comparatively limited.

Main components

The core architecture of Alt-Ergo comprises three main elements: a depth-first search (DFS)-based SAT solver, a quantifiers instantiation engine that uses e-matching, and an assembly of decision procedures for a range of built-in theories. These components collectively enable Alt-Ergo's abilities in automatic formula solving.

Built-in theories

Alt-Ergo implements (semi-)decision procedures for the following theories:

• Empty theory
• Linear integer arithmetic
• Linear rational arithmetic
• Non-linear arithmetic
• Floating point arithmetic
• Polymorphic arrays
• Enumerated data types
• AC symbols
• Record data types

Industrial uses

Several verification platforms are built on Alt-Ergo:

• Why3, a platform for deductive program verification, uses Alt-Ergo as main prover^[2]
• CAVEAT, a C-verifier developed by CEA and used by Airbus; Alt-Ergo was included in the qualification DO-178C of one of its aircraft
• Frama-C, a framework to analyse C-code, uses Alt-Ergo in the Jessie and WP plugins (dedicated to deductive program verification)
• SPARK, uses Alt-Ergo (behind GNATprove) to automate the verification of some assertions in Spark 2014
• Atelier-B can use Alt-Ergo instead of its main prover (raising success from 84% to 98% on ANR Bware project benchmarks)
• Rodin, a B-method framework developed by Systerel, can use Alt-Ergo as a back-end
• Cubicle, an open source model checker to verify safety properties of array-based transition systems
• EasyCrypt, a toolset for reasoning about relational properties of probabilistic computations with adversarial code
• BWARE^[3]
• Cafein^[3]
• FUI Hi-Lite^[3]
• Decert^[3]
• ADT Alt-Ergo^[3]
• A3PAT^[3]

See also

• Formal verification
• Z3 Theorem Prover

External links

• , OcamlPro
• Alt-Ergo at LRI

Notes and References

1. Web site: About . 2023-06-15 . alt-ergo.ocamlpro.com.
2. Web site: Why3 . 2023-06-15 . why3.lri.fr.
3. Web site: The Alt-Ergo Theorem Prover: Academic Web Page . 2023-06-15 . alt-ergo.lri.fr.