Nice to see someone with legal qualifications actually speak about this.
For the question:
My impression is "yes" -- for instance, the evaluation function is a "portion" (indeed, quite a large one), and [for the purposes here] the evaluation function of Rybka can be considered a "modification" of that of Fruit (I realise the extent of this claim would need to be carefully delineated, but trying to do so here would reduce the discussion to one of a more technical nature). Others might say that the "modification" as meant by the GPL should be construed largely in the sense of copy/paste (this is a common armchair opinion about GPL issues, though I can't speak to its validity). In any event, whether or not such a "modification" can be construed to have been done in such a way (e.g. "clean room", as per CW) so as to skirt the GPL issue is yet another question.Does Rybka 1 Beta include a verbatim “portion” or a “modified” “portion” of Fruit 2.1?
Here is a random opinion: http://www.iusmentis.com/computerprogra ... ty-threat/
Basing a product on open source software
The GPL permits distribution of works that are based on a work under the GPL only if such distribution is done under the terms of the GPL as well. There is unfortunately no clear definition of what exactly constitutes "based on". The straightforward case is when source code from a work under the GPL is copied into another application. Statically linking several modules together to create an application would also seem to be covered. Dynamically linking two modules together is already a quite controversial case and by using technologies such as CORBA, RPCs, sockets or plug-in modules the situations can grow quite complex very quickly.
There is no clear consensus on the interpretation of the GPL. An often heard compromise is to assume that any form of linking invokes the sublicensing clause, but using inter-process communication does not. It should however be noted that using such technologies merely to avoid the consequences of the GPL will not be appreciated by the courts.
The Library GPL and the MPL are less problematic. It is permitted to create a "larger work" by combining the work under the MPL or LGPL with other software. This larger work may then be distributed under any licensing terms, as long as the conditions of the MPL or LGPL are adhered to for the portions of the larger work which were originally obtained under those licenses. This means that the source code of these parts have to be made available, including any modifications, and the authors of these parts must be credited in the documentation of the larger work.