174GNU GENERAL PUBLIC LICENSEVersion 2, June 1991 Copyright (C) 1989, 1991 Free Software Foundation, Inc.59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Everyone is permitted to copy and distribute verbatim copies of this licensedocument, but changing it is not allowed.PreambleThe licenses for most software are designed to take away your freedom toshare and change it. By contrast, the GNU General Public License is intendedto guarantee your freedom to share and change free software—to make surethe software is free for all its users. This General Public License applies to mostof the Free Software Foundationʼs software and to any other program whoseauthors commit to using it. (Some other Free Software Foundation software iscovered by the GNU Library General Public License instead.) You can apply itto your programs, too.When we speak of free software, we are referring to freedom, not price. OurGeneral Public Licenses are designed to make sure that you have the freedomto distribute copies of free software (and charge for this service if you wish), thatyou receive source code or can get it if you want it, that you can change thesoftware or use pieces of it in new free programs; and that you know you can dothese things.To protect your rights, we need to make restrictions that forbid anyone to denyyou these rights or to ask you to surrender the rights. These restrictionstranslate to certain responsibilities for you if you distribute copies of thesoftware, or if you modify it.For example, if you distribute copies of such a program, whether gratis or for afee, you must give the recipients all the rights that you have. You must makesure that they, too, receive or can get the source code. And you must showthem these terms so they know their rights.We protect your rights with two steps: (1) copyright the software, and (2) offeryou this license which gives you legal permission to copy, distribute and/ormodify the software.Also, for each authorʼs protection and ours, we want to make certain thateveryone understands that there is no warranty for this free software. If thesoftware is modified by someone else and passed on, we want its recipients toknow that what they have is not the original, so that any problems introduced byothers will not reflect on the original authorsʼ reputations.Finally, any free program is threatened constantly by software patents. Wewish to avoid the danger that redistributors of a free program will individuallyobtain patent licenses, in effect making the program proprietary. 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