[theK]

I find it terrifying that this type of reasoning is actually legitimate law.

Think about all the drive by licensing felonies everyone has comitted by accidentally reading open core code and then, at a later point implementing something vaguely related....

EDIT: Typos & punctuation

[rahoulb]

IANAL but that's why law has to be interpreted by judges rather than being a book of absolute rules.

Lots of codified laws are bent or modified by prevailing social attitudes, customs or precedent, so you could argue "I looked at it a couple of years ago and then independently decided to implement something similar" is a very different situation to "we read through the code and a week later started on a competitor".

Whether you'd get away with it is another matter, depending upon interpretation and perspective.

[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.