License is granted to copy or use this document according to the Open Public License (OPL, enclosed below), which is a Public License, developed by the GNU Foundation, which applies to ``open source'' generic documents.
In addition there are three modifications to the OPL:
Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder. (This is to prevent errors from being introduced which would reflect badly on the author's professional abilities.)
Distribution of the work or derivative of the work in any standard (paper) book form is prohibited unless prior permission is obtained from the copyright holder. (This is so that the author can make at least some money if this work is republished as a textbook or set of notes and sold commercially for - somebody's - profit. The author doesn't care about copies photocopied or locally printed and distributed free or at cost to students to support a course, except as far as the next clause is concerned.)
The "Beverage" modification listed below applies to all non-Duke usage of these notes in any form (online or in a paper publication). Note that this modification is probably not legally defensible and can be followed really pretty much according to the honor rule.
As to my personal preferences in beverages, red wine is great, beer is delightful, and Coca Cola or coffee or tea or even milk acceptable to those who for religious or personal reasons wish to avoid stressing my liver. Students at Duke, whether in my class or not, of course, are automatically exempt from the beverage modification. It can be presumed that the fraction of their tuition that goes to pay my salary counts for any number of beverages.