[singron]

The clean room described above is a fairly bullet proof technique, but it's only been employed very few times and is not necessary to create an original work. Nearly every work was produced by people who were exposed to other copyrighted works. Unless something is a straightforward copy, it's a high burden to show that something is effectively a copy or translation. A lot of these kinds of things are untested in court probably because it's so difficult to make an abstract case.