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clasp is an answer set solver for (extended) normal and disjunctive logic programs. It is part of the Potassco project for Answer Set Programming (ASP). The primary algorithm of clasp relies on conflict-driven nogood learning, a technique that proved very successful for satisfiability checking (SAT). clasp has been genuinely developed for answer set solving but can also be applied as a (Max-)SAT or PB solver or as a C++ library in another program. It provides different reasoning modes and other advanced features including:

Detailed information (including a User's manual), source code, and pre-compiled binaries are available at:


clasp is distributed under the MIT License.

See LICENSE for details regarding the license.


LICENSE        - The MIT License
CHANGES        - Major changes between versions      - This file
CMakeLists.txt - Configuration file for building clasp with CMake
cmake/         - Module directory for additional CMake scripts
app/           - Source code directory of the command-line interface
clasp/         - Header directory of the clasp library
src/           - Source code directory of the clasp library
tests/         - Unit tests of the clasp library
examples/      - Examples using the clasp library
libpotassco/   - Directory of the potassco library
tools/         - Some additional files


The preferred way to build clasp is to use CMake version 3.1 or later together with a C++ compiler that supports C++11.

The following options can be used to configure the build:

CLASP_BUILD_APP         : whether or not to build the clasp application
CLASP_BUILD_TESTS       : whether or not to build clasp unit tests
CLASP_BUILD_EXAMPLES    : whether or not to build examples
CLASP_BUILD_WITH_THREADS: whether or not to build clasp with threading support
                          (requires C++11)

For example, to build clasp in release mode in directory <dir>:

cmake -H. -B<dir>
cmake --build <dir>

To install clasp afterwards:

cmake --build <dir> --target install

To set the installation prefix, run cmake with option -DCMAKE_INSTALL_PREFIX=<path>.

Finally, you can always skip installation and simply copy the clasp executable to a directory of your choice.


A User's Guide is available from

Source code documentation can be generated with Doxygen. Either explicitly:

cd libclasp/doc/api
doxygen clasp.doxy

or via the doc_clasp target when using cmake.


clasp reads problem instances either from stdin, e.g

cat problem | clasp

or from a given file, e.g

clasp problem


clasp --help

to get a basic overview of options supported by clasp or

clasp --help={2,3}

for a more detailed list.

In addition to printing status information, clasp also provides information about the computation via its exit status. The exit status is either one or a combination of:

0  : search was not started because of some option (e.g. '--help')
1  : search was interrupted
10 : problem was found to be satisfiable
20 : problem was proved to be unsatisfiable

Exit codes 1 and 11 indicate that search was interrupted before the final result was computed. Exit code 30 indicates that either all models were found (enumeration), optimality was proved (optimization), or all consequences were computed (cautious/brave reasoning). Finally, exit codes greater than 32 are used to signal errors.


⚙️ A conflict-driven nogood learning answer set solver







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