@unpublished{purdue2004,
 author = {J. M. Siskind},
 title = {Algorithmic Differentiation of Functional Programs},
 location = {Purdue University},
 date = 16,
 month = jun,
 year = 2004,
 url = {http://engineering.purdue.edu/~qobi/tweet-talks/purdue2004-slides.pdf}}