E.1.1 The SWI-Prolog Prolog libraries

Lacking a satisfactory technical solution to handle article 6 of the LGPL, this license cannot be used for the Prolog source code that is part of the SWI-Prolog system (both libraries and kernel code). This situation is comparable to libgcc, the runtime library used with the GNU C compiler. Therefore, we use the same proven license terms as this library. The libgcc license is the with a special exception. Below we rephrase this exception adjusted to our needs:

As a special exception, if you link this library with other files, compiled with a Free Software compiler, to produce an executable, this library does not by itself cause the resulting executable to be covered by the GNU General Public License. This exception does not, however, invalidate any other reasons why the executable file might be covered by the GNU General Public License.