NACRE : Nogood And Clause Reasoning Engine
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NACRE: Nogood And Clause Reasoning Engine


NACRE is a constraint solver written in C++. The main purpose of this solver is to experiment nogood recording (with a clause reasoning engine) in Constraint Programming (CP). In particular, the data structures of the solver have been carefully designed to play around nogoods and clauses. This is the first version of the solver and it has been submitted to the XCSP3 2018 competition under the CSP MiniTrack. NACRE took first place!


Go to the core folder and use the following line:


You can add -j for parallel compilation. It will compile both the parser and solver.

The executable will be in that folder under the name nacre_mini_release

For help, call the executable without any parameters, use the following option for details:


Even for default configuration you need to specify the resolution method. In NACRE, there are currently 4 methods:

  • -complete: standard MAC approach
  • -incng: Increasing Nogoods (Increasing Nogoods in Restart-Based Search, Jimmy H. M. Lee, Christian Schulte,Zichen Zhu, 2016)
  • -nld: Negative last-decision nogoods (Recording and minimizing nogoods from restarts, Christophe Lecoutre, Lakhdar Sais, Sébastien Tabary, Vincent Vidal, 2007)
  • -ca: Conflict analysis, SAT-based lazy explanations


This work has been supported by the project CPER Data from the region ” Hauts-de-France”.

This solver is produced for my (Gaël Glorian) PhD thesis work on data structures designed for clause-based nogood recording.

A big thank-you to Gilles Audemard, for his support and help.