Lingeling

Lingeling is a high-performance, open-source SAT solver for propositional logic, developed by Armin Biere at Johannes Kepler University Linz in Austria. It solves CNF formulas using a modern CDCL (conflict-driven clause learning) approach with restarts, aggressive preprocessing, and configurable heuristics. Lingeling is designed to be fast and memory-efficient, and it provides a wide range of command-line options to tune solver behavior for different classes of formulas.

Lingeling is part of a family of solvers derived from the same code base. The base solver Lingeling is single-threaded, while parallel variants such as Plingeling and Treengeling extend the approach to multi-core and multi-instance configurations: Plingeling runs several Lingeling instances in parallel and shares information between them, and Treengeling uses a multi-threaded or distributed setup to utilize multiple cores. These parallel solvers have been used to achieve strong results in SAT competitions and in portfolio-based solving.

In practice, Lingeling is used in research, benchmarking, and technology evaluation. It accepts standard CNF input, supports various preprocessing steps and incremental solving modes, and can be integrated into solver portfolios or used in experimental pipelines. The project is open source and publicly available, and its development has influenced subsequent SAT solvers and portfolio systems.