I believe that Pilgrim here does not understand very well how copyright works:

> Their claim that it is a "complete rewrite" is irrelevant, since they had ample exposure to the originally licensed code

This is simply not true. The reason why the "clean room" concept exists is precisely since actually the law recognizes that independent implementations ARE possibile. The "clean room" thing is a trick to make the litigation simpler, it is NOT required that you are not exposed to the original code. For instance, Linux was implemented even if Linus and other devs where well aware of Unix internals. The law really mandates this: does the new code copy something that was in the original one? The clean room trick makes it simpler to say, it is not possible, if there are similar things it is just by accident. But it is NOT a requirement.