In as few words as possible

[Michael Sherwin]

According to the GPL that comes with Fruit.

As soon as Vasik and Juri released programs that were derived from Fruit then they agreed to the GPL. Once they agree to the GPL they are bound by it. It then leaves the realm of copyright law and enters the realm of contract law.

The only question that remains is if this type license is valid under the law.

[hgm]

It is not.

[Michael Sherwin]

It is not.

Then we too are in agreement, because, I also believe that it is not!

[hristo]

According to the GPL that comes with Fruit.

As soon as Vasik and Juri released programs that were derived from Fruit then they agreed to the GPL. Once they agree to the GPL they are bound by it. It then leaves the realm of copyright law and enters the realm of contract law.

This only applies if their work is derivative of the original.
They are not bound by GPL if the respective products aren't derivatives.

The only question that remains is if this type license is valid under the law.

The 'only' question that remains is "What is a derivative work?", the GPL is valid under law so far as we know.

Regards.

[Alessandro Scotti]

The GPL license is valid under the law, and has already been tested in court several times. If GPL license is not valid then you would not be able to use GPL'ed code anyway as nothing (but the GPL) grants you the right to use it.

Doing a rewrite of a GPL program is not an infringement though, as you end up with a completely different beast. Such a program cannot be considered a derivative.

A lot of important GPL projects are in fact reimplementations of commercial projects, and many of those have had to use reverse engineering techniques in order to achieve this. It can be easily argued that Wine is a derivative of the Win32 subsystem, from which it takes all external data structures and interfaces (not to mention semantics), but it's been completely rewritten so it's not a clone or so, but a perfectly legit and GPL'able software.

[Michael Sherwin]

We are going in circles here. If I never saw another chess program other than Fruit and I wanted to write a chess program, so I used Fruit as a guide then my program is derived from Fruit. If anyone asked me, 'where did you derive the knowledge from to write your own program', then I would have to answear that I derived it from Fruit. Therefore Rybka is a derivitive of Fruit. However, the GPL does not apply, because, there is nothing original in Fruit and I can quote the author himself as saying that there is nothing original.

So, in the case of Fruit at least the GPL may not be valid under the law.

[Dann Corbit]

We are going in circles here. If I never saw another chess program other than Fruit and I wanted to write a chess program, so I used Fruit as a guide then my program is derived from Fruit. If anyone asked me, 'where did you derive the knowledge from to write your own program', then I would have to answear that I derived it from Fruit. Therefore Rybka is a derivitive of Fruit. However, the GPL does not apply, because, there is nothing original in Fruit and I can quote the author himself as saying that there is nothing original.

So, in the case of Fruit at least the GPL may not be valid under the law.

If this were true, then anyone who had read the source of Fruit (or any other GPL program) and writes a program that uses something he has learned is writing a GPL program. And if that is true, then GPL is viral in a horrible way beyond any imagining.

It is like saying, "If you have read my book and later write your book on the same subject, then your book also belongs to me."

[Dann Corbit]

And on the other side of the issue, imagine a book.
In our book we write a story.
In our story there is a plot and characters.

There in nothing original about any of that. The words (taken one at a time) are not original. The plot is not original. Even the characters are not original. But the whole thing (taken as a whole is original). This highly unoriginal work is still subject to copyright. And if I take that unoriginal work and change a few lines, I cannot call it my own work.

You cannot copyright math. You cannot copyright an idea. You cannot copyright an algorithm. You can copyright your implementation of an algorithm. You can copyright your implementation of a plot.

What is legal and what is moral may or may not coincide. And what I consider moral and what I consider legal may or may not coincide. For instance, I do not like software patents (though I would not knowingly violate one because my respect for the law is greater than my dislike of software patents).

[Alessandro Scotti]

As H.G. explained elsewhere, it's not your definition of derivative that counts, but the legal one. To show that a program is derivative of another, you must usually show that the former contains some portions (code) of the latter.
If you look at Fruit and learn enough to write your own chess program then fine, as long as you don't borrow code from Fruit then it's not a derivative, even if everything it contains you learned from Fruit.
That Fruit is not original by the way is simply untrue, it contains many great ideas that nobody before Fabien know how to implement correctly. And to bring an idea to reality, it's by itself a difficult and creative job. The famous LZW patent (GIF, modem compression, etc.) covered an implementation made by Welch of an algorithm by Lempel and Ziv. The algorithm itself was not patented, yet the implementation was so brilliant that it became THE implementation for LZ78 (LZ77, fortunately for most of the world, got a patent free implementation courtesy of Mark Adler and Jean L. Gailly).
Anyway I'm digressing. In Fruit, the GPL covers Fruit's code. That is 100% original and written by Fabien. You copy even a small but significant part of it and you infringe, you reimplement independently the underlying ideas and you're ok.

[Michael Sherwin]

As H.G. explained elsewhere, it's not your definition of derivative that counts, but the legal one. To show that a program is derivative of another, you must usually show that the former contains some portions (code) of the latter.
If you look at Fruit and learn enough to write your own chess program then fine, as long as you don't borrow code from Fruit then it's not a derivative, even if everything it contains you learned from Fruit.
That Fruit is not original by the way is simply untrue, it contains many great ideas that nobody before Fabien know how to implement correctly. And to bring an idea to reality, it's by itself a difficult and creative job. The famous LZW patent (GIF, modem compression, etc.) covered an implementation made by Welch of an algorithm by Lempel and Ziv. The algorithm itself was not patented, yet the implementation was so brilliant that it became THE implementation for LZ78 (LZ77, fortunately for most of the world, got a patent free implementation courtesy of Mark Adler and Jean L. Gailly).
Anyway I'm digressing. In Fruit, the GPL covers Fruit's code. That is 100% original and written by Fabien. You copy even a small but significant part of it and you infringe, you reimplement independently the underlying ideas and you're ok.

So the type of derivation matters! But, then again the law is always open to reinterpretation! At the next court case the definition of derivation as applies to the GPL can change!