Steve Jenson's blog

Uh oh!! The Half-Life 2 source, leaked the other day, apparently has references to Quake source, which was released under the GPL. Now, id will sell anybody with enough money a Quake license, and the original Half-Life did have a license but it's been well touted that Valve's new game engine for Half-Life 2 (called Valve Source™) would be entirely non-derivative since they want to license their work to others and make a large pile of money.

At least one game has already been sold a license to Valve Source™

So, if Valve did not license Quake from id, does that mean they've implicitly agreed to use the GPL'd version? That would make Valve Source™ GPL'd. If so, does that mean that under section 3b of the GPL, that all we need to do is request the souce from Valve and they'll be required by law to give it out? I know that's legally dubious at best. I'm just curious.