Posted by Borneq on Jan 25, 2012; 11:33am
URL: https://forum.librecad.org/Different-versions-of-GPL-tp5429963.html

dxflib of RibbonSoft is under GNU General Public License version 2, LibreDWG is under GNU General Public License version 3 (or at you option any later version). How link code under two version of GPL?
GPL can't linked with non-free code but:
in GLP v2 is:
" 10. If you wish to incorporate parts of the Program into other free
programs whose distribution conditions are different, write to the author
to ask for permission.  For software which is copyrighted by the Free
Software Foundation, write to the Free Software Foundation; we sometimes
make exceptions for this.  Our decision will be guided by the two goals
of preserving the free status of all derivatives of our free software and
of promoting the sharing and reuse of software generally."

In http://www.gnu.org/licenses/rms-why-gplv3.html is:
"When we say that GPLv2 and GPLv3 are incompatible, it means there is no legal way to combine code under GPLv2 with code under GPLv3 in a single program. This is because both GPLv2 and GPLv3 are copyleft licenses: each of them says, “If you include code under this license in a larger program, the larger program must be under this license too.” There is no way to make them compatible. We could add a GPLv2-compatibility clause to GPLv3, but it wouldn't do the job, because GPLv2 would need a similar clause."