English: compatibility of common open-source software licenses 2007. Software may be combined under a license that can be reached by tracking the arrows forward from the licenses of all its components. The result must then carry the license in the target box, possibly with additions from the source licenses. Permissive licenses allow the software to become non-free, protective (copyleft) licenses prevent the component from becoming non-free, weakly protective (weak copyleft) licenses additionally allow it (often a software library) to be part of a larger non-free work.