@unpublished{nepls2008,
 author = {J. M. Siskind},
 title = {Automatic Differentiation of Functional Programs or Lambda the Ultimate
          Calculus},
 location = {New England Programming Languages and Systems (NEPLS)},
 date = 21,
 month = nov,
 year = 2008,
 url = {http://engineering.purdue.edu/~qobi/tweet-talks/nepls2008-slides.pdf}}