[saidajigumi]

You are misinterpreting "reciprocity"; it has nothing to do with Artifex's dual-licensing arrangement. If you read the linked PDF, you'll find this:

Reciprocity means a mutual or cooperative interchange of favors or privileges. Something is reciprocal when it is performed, experienced, or felt by both sides. (The American Heritage Dictionary of the English Language, 4th edition.)

The GPL license is reciprocal, because it is “performed, experienced, or felt” by both sides—the licensor and the licensees both use the GPL.

In non-legal terms, I'd put this as "the GPL allows you to redistribute in kind: by extending the offer the original licensor made to others." The "price" of redistribution is agreeing to public participation in the co-evolution of the software.

This is not to be confused with Artifex's offer to dual-license: you may either accept the terms of the GPL or purchase a commercial license. These two worlds do not interact other than Artifex, the copyright holder, uses its rights under copyright law to offer these two alternatives.

[10165]

Yes, the "outcome" to which I was referring was in fact the effect of dual-licensing.

With respect to the book chapter, as I interpret it, reciprocity includes asking for the licensee to open source their work. But I leave this to the experts to interpret definitively.

Assuming I am not misunderstanding, if the licensee "reciprocates", then there is no closed source and the "problem" I am alluding to goes away. Because users can now see the source code and theoretically they can determine where it came from.

(The problem being that GPL source code and the value thereof is sometimes "concealed" in closed source products. This is just my personal view. I may care about things that others do not. Opinions may differ.)

[lolc]

You cannot have GPL-licensed code in closed-source code. It's a violation of the license so the code ceases to be GPL-licensed and becomes unlicensed. If you distribute that code, in source or binary form, you can get sued by the copyright holders which is what this case is about.

[eru]

You can totally have GPL-licensed code in closed-source code as long as you don't publish it. So you can totally run your SaaS business like that.

The Affero GPL tries to close that loophole.

[lolc]

Indeed the code only becomes unlicensed as soon as you violate the GPL terms. So I guess the correct way of framing this would be that internal copies, including changes, are still under the GPL.

[fourthark]

You can if it is dual-licensed.

[lolc]

Then it's licensed under some other license and the GPL does not apply. If I rent a building and the building is for sale I still don't own it until I close that contract.

If I copy GPL-licensed code without following the license terms, the GPL no longer applies and the code becomes unlicensed. The GPL is explicit about that.

If I acquire code under another license than the GPL my copy is not GPL-licensed even if it's available under the GPL license. Ultimately, the GPL requires that all people who pass on code under the GPL adhere to its terms. If one person in the chain didn't (for example by not making available the source) all subsequent copies become unlicensed.