What is Copyleft?

Dave J Woolley david.woolley at bts.co.uk
Fri Feb 23 20:23:01 UTC 2001

> From:	Frank Hecker [SMTP:frank at collab.net]
> makes a distinction between licenses that are "copyleft" licenses,
> licenses that are "not a strong copyleft", and "non-copyleft" licenses.
> Thus the GPL is described as a "copyleft license", but the LGPL is
> described as "not a strong copyleft license, because it permits linking
> with non-free modules"; the MPL (which permits both static and dynamic
I had a look over the LGPL and it seems to have some interesting
restrictions on derivative works that are almost certainly 
violated more often than obeyed, at least for the glibc.
It seems to require that limited licesnses be given to modify 
the code and to reverse engineer it to aid in modifying it. There
are also requirements with regard to notifying the library copyright.

As I read it, if you want to completely avoid restrictions, you
must distribute the proprietory code as unlinked object files
and let the end user create the final executable.  (This only
works for the LGPL as it contains exemptions for common uses of
header files.)

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