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A copyleft patent is increasingly being suggested for patents, especially in the context of the struggle for software patents in the European Union. Template:Lopsided Copyleft patents hinge on a patent law framework rather than a copyright law framework. Proposals include the open patent pools that allow royalty-free use of patents contributed to the pool under certain conditions. Conditions include surrendering the right to apply for new patents that are not contributed to the pool. This has not taken off, perhaps in part because patents are relatively expensive to obtain, whereas copyright is obtained for no cost.
Since for most copylefted creations the copyleft characteristic is however only secured by copyright law, patenting mechanisms can threaten the copyleft freedoms attached to such creations, when patent law is allowed to overrule copyright (or in any other way limit the free expansion of copylefted creations), which might be the case for the new rules regarding patents developed in the European Union in the early 21st century (see also article on Community patent). There seems to be no easy answer to such threats, while it is considered that generally communities developing copylefted products have neither the resources nor the organization for complex patenting procedures. However, an organized answer to such issues seems to start emerging from places like Groklaw. Also IBM could be considered by the open source community as rather an ally, when it comes to combining traditional copyright protection for copylefted creations with patented inventions, see: Infoworld article notifying that IBM says it won't assert patents against Linux kernel