Suppose (for the sake of argument) that the IPPOLIT developers formed their product by: creating a "Rybka 3 emulator", and then modifying this. There are two components here as to copyright law. The first is whether the creation of the emulator was done in a legal way; the second (applied if the first is not the case) is whether the modifications are substantial enough to make it "original". I stress the first item because, in theory, they could even sell the "Rybka 3 Emulator" if it were formed in a legal manner (not sure anyone would buy it, but).
Similarly, for the sake of argument, let's say VR made a "Fruit 2.1 emulator" (at least of the evaluation function) on top of his Rybka 1.6(?) bitboard code, and then proceeded to modify it. Same logic applies, and let's assume that the "modifications" are deemed insubstantial from the standpoint of copyright law. The gist of all this is the following: the emulator has now become an affirmative defense for VR (that is, "Yes, what you say is true, Rybka does "derive" from Fruit, but that is not relevant because..."), and affirmative defenses reverse the burden of proof, that is, now VR would have to show that he had made this "Fruit 2.1 emulator" in a legal manner. Given his history with old code, would he likely be able to do this?
Again, I'm just randomly speculating on some (possible) legal aspects, and/or pitfalls in the road ahead.
