Legislative Decree
The term copyleft is a play on words that can be translated as left copy or permitted copying, contrary to the meaning of copyright which literally means right to copy. He is considered that a free license is copyleft when apart from granting permission for use, copying, modification, and redistribution of the protected work, it contains a clause which imposes a similar or compatible license, copies and derivative works. The development of new technologies and the need for cooperation between the creators of computer programs globally to course the need to establish a new type of social pact. If copyright was intended to restrict access to private and protected the exclusive exploitation of works in favour of the holder of this right, copyleft is a reverse method and aims to keep these free creations demanding at the same time that all later versions changed and deriving from them are also distributed as free. In this way is intended to ensure the freedom of those who they participate in communal form in the production of free programs or other intellectual resources under the copyleft license. However, the difference between free and proprietary software is not so great, in the sense that both need a license.
The difference is what allows each one of the licenses. In accordance with the Spanish legislation (Royal Legislative Decree 1/1996 of April 12, which approves the revised text of the intellectual property law) and international treaties not to exploit a program without the express consent of its holder which usually does so through a license. But license does not always imply a transfer of ownership but the granting of specific rights enjoyed by the author. In proprietary right these are normally rights of use and in the case of free software also distribution and modification as well as defend some producer rights or obligation to keep free software in each of its correlative versions.