Re: Question: using public domain code?

[Qiantan Hong]

In such case (code says PD but actually CC0 like), does it
prevent usage in GNU project without copyright papers?

To my understanding the copyright papers are to anticipate
upgrading to new license in the future.
AFAIK CC0-like are compatible with GPL,
does that mean it doesn’t create trouble for license upgrading even
without copyright papers? 
(Because the CC0-like code doesn’t need to be relicensed,
we just need to relicense the other part of the codebase and
those CC0 like code will still stay compatible?)

> On Sep 7, 2021, at 5:32 AM, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
> 
>> But I’m unsure about public domain...
> 
> In theory, public domain can be used, and I think we wpouldn't require
> copyright papers to use it in Emacs.
> 
> *BUT* in practice, there is pretty much no ELisp code in the public
> domain.  If the file says that it's in the public domain, it's usually
> a misunderstanding on the part of the authors thinking they can opt to
> put the file in the public domain, which is not the case.
> 
> You can assume they meant to use something like the CC0 license, instead.
> 
> 
>        Stefan
> 
>