If somebody has participated in an open source project, and has previously contributed several lines of source code but all those lines have now been completely rewritten and/or deleted so that all earlier contributions by that person have been effectively erased, does that person still hold copyright on the derivative work?

I.e., certainly a full rewrite of a project will assign all copyright to those who have contributed to the rewrite only, but does this apply to individual contributions within a project as well?

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    Closely related: Theseus' Paradox applied to code copyright -- it is quite difficult to know what aspects of a program are copyrightable. For example, if you do a complete rewrite of the Harry Potter book series, even while not referring to the original text and trying to avoid verbatim copying, it's hard to imagine your new work is not infringing. However, the order and structure of mechanical steps performed by a computer program might (or not) be protected differently. – apsillers Apr 20 at 13:38
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    To address your concern specifically, it depends on the substantiality of what remains, structurally, of your contribution after the literal code is removed and the degree to which that structure constitutes protectable expression under copyright. (But this guideline isn't much of an answer by itself.) – apsillers Apr 20 at 13:45

I think my esteemed colleague has said all that's really necessary in comments supra, but it would be good to have this in an answer. The question you ask is known, philosophically, as that of the Ship of Theseus: if you replace all the parts of a thing, is it any longer the original thing?

I am not aware of any definitive answers in copyright jurisprudence. We address the question in a number of places on this site, including (but not limited to) here, here, here, and here. My personal view on this is that, unless special care is taken, even a complete reimplementation may well create a copyright derivative of the earlier work, and the rights holders of the earlier work will continue to have a rights interest in the reimplementation.

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