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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.
This article is provided by FOLDOC - Free Online Dictionary of Computing (


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.
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References in periodicals archive ?
Open source also 'emphasizes the centrality of novel forms of coordination' over copyleft licensing or releasing source code (Kelty, 2008: Loc.
Computer programs is an example of a work in which the copyright holder usually places restrictions on the reproduction, adaptation or distribution of the work (computer program.) Should a copyright holder of a specific computer program choose to however, she may through a copyleft licensing scheme, give every person who receives a copy of a work permission to reproduce, adapt or distribute the computer program as long as any resulting copies or adaptations are also bound by the same copyleft licensing scheme.
While knowing how open source projects operate and organize into complex networks may be interesting from a social and economic perspective, there are other implications of network science that are more relevant to the legal field, and that is in the area of copyleft licensing. Copyleft is a legal concept drafted by programmer Richard Stallman, which allows the further distribution and modification of software released under the terms of a copyleft licence, but it does not allow proprietary developers to come and "close" the released software by not offering access to the source code.
GNU/Linux is based on a copyleft licensing system, which specifies not only that all of the GNU/Linux code is open -- that is, completely viewable to, and copyable by, anyone -- but that anyone who makes an addition or otherwise modifies the underlying code must make their code available according to the same copyleft license.
The company says it is still working out details of what it means by open source development for Digitalme, but there will some sort of web site where code can be downloaded and returned on a copyleft licensing model.
of the LGPL, most likely in an attempt to prevent copyleft licensing