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Re: Strong Copyleft licenses other than the GNU GPL family.

Le quartidi 14 brumaire, an CCXXIV, Mario Castelán Castro a écrit :
> By strong Copyleft I mean a free software license that requires "derivate
> works" (as determined by Copyright law) to be free software (as in freedom),
> including works that are derivatives by making use of the Copylefted work
> through an API.

This kind of license, if it exists or if someone invents it, would have two
serious drawbacks. That may explain why you do not find one.

The firs drawback is that it would be incompatible with GPL code and
libraries, and even possibly LGPL. That means libraries made using that
license can not be used from GPL code or with GPL libraries. Basically,
there is logically room for only one widely-adopted copyleft license.

The second drawback is that it would probably have no legal standing.
Copyleft is based on copyright, and copyright controls distribution, nothing
else. In principle, it can not control API use, since there is no
distribution involved. In practice, you can argue that using an API requires
copying tiny bits of it in the calling program: function names, macro
expansion, etc. But this claim is weak: copyright requires originality, and
there is little room for originality in function names; and it is easy to
circumvent. The more restrictive you make your license, the stronger the
incentive to circumvent it.


  Nicolas George

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