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/kop'ee-left/ (A play on "copyright") The copyright notice and General Public License applying to the works of the Free Software Foundation, granting reuse and reproduction rights to everyone.

Typically copyrights take away freedoms; copyleft preserves them. It is a legal instrument that requires those who pass on a program to include the rights to use, modify, and redistribute the code; the code and the freedoms become legally inseparable.

The copyleft used by the GNU Project combines a regular copyright notice and the "GNU General Public License" (GPL). The GPL is a copying license which basically says that you have the aforementioned freedoms. The license is included in each GNU source code distribution and manual.

See also General Public Virus.


A requirement in the GNU GPL software license and other "free" software licenses that anyone who redistributes the software does so under the same license and also includes the source code. The "free" means free of restrictions (see free software). The copyleft clauses were written to support copyright laws, not eliminate them.

Strong Vs. Weak
A "strong copyleft" license, such as the GNU GPL license, applies to all derived works and software components in the package. A "weak copyleft" license, such as the GNU Lesser GPL, applies only to the original copylefted work.

Full Vs. Partial
"Full copyleft" means that all of the work may be modified, whereas "partial copyleft" restricts some parts of the work from being altered. See GNU General Public License and copyright.
References in periodicals archive ?
One of the effects of copyleft licensing is that it may generate long chains of distributions in which software projects may fork into others, with the originating source code becoming entangled in licensing webs.
Under both copyleft licenses such as GPLv2, and non-copyleft attribution-only licenses, the FOSS movement produces software with a decentralized development methodology relying on source code transparency and Internet-coordinated activity.
For speculation on who first coined the term, see Wikipedia, Copyleft, http://en.
It then explains how this idea of copyleft works, how it began, and why its proponents encourage its widespread use to satisfy the disconnect existing between current intellectual property laws and common Internet practices.
GNU General Public License has emerged as a default copyleft license 7
169) As such, we harness the network effects of OIC distributed cost and benefit structures, the commitment to OIC values, and the reliability of other standard distributed OIC licenses, such as the GPL or Creative Commons' copyleft licenses, and apply them in the patent context.
Vetter, Claiming Copyleft in Open Source Software: What if the Free Software Foundation's General Public License (GPL) Had Been Patented?
One copyleft license is enough, they argued, particularly when the GPL has such a large user base.
12) E, embora a segmentação, em linhas gerais, reflita a adotada pelas emissoras FM, grande parte dos podcasts se alimenta de músicas licenciadas para livre reprodução - em vez do copyright, ou direito autoral, estes trabalhos são protegidos por copyleft, referência ao projeto Creative Commons.
In fact, the Copyleft approach allows the author to retain her copyrights, and use those rights to ensure that subsequent recipients use her work in the way that she wants.
LOS ANGELES, June 2 /PRNewswire/ -- dropping knowledge, a global initiative to turn apathy into activity through the simple act of asking questions, released its latest CopyLeft film "What's Your Tree?
But Linux is copyrighted, and distributed under a novel and controversial GNU Public License (GPL), sometimes referred to as copyleft.