Here is Yahoo's index to several documents giving information on US (and other) copyright laws. Of particular interest is the Fair Use clause in the United States Code, title 17 (Copyright act of 1976, most recently amended on Jan 5, 2009.), which mentions that fair use for teaching or research is not an infringement of copyright. (This is just a paraphrase, which is not 100% correct.) Check out the full text.
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