@unpublished{nips2008,
 author = {J. M. Siskind},
 title = {AD for Probabilistic Programming},
 location = {NIPS Workshop on Probabilistic Programming: Universal
             Languages and Inference; systems; and applications},
 date = 13,
 month = dec,
 year = 2008,
 url = {http://engineering.purdue.edu/~qobi/tweet-talks/nips2008-slides.pdf}}