Creative Commons Attribution-Share Alike 3.0 United States License

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<a rel="license" href="http://creativecommons.org/licenses/by-sa/3.0/us/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-sa/3.0/us/88x31.png"/></a><br/>This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-sa/3.0/us/">Creative Commons Attribution-Share Alike 3.0 United States License</a>.

This particular license allows redistribution and modification and use for any purpose (including commercial) but requires that the author's attribution be maintained.