In Fukuda et al. (eds) "Proceedings of ICMS 2010", Springer LNCS vol. 6327,
2010.
This is superseded by the corresponding full paper
@INPROCEEDINGS{harrison-picka, author = "John Harrison", title = "A formal proof of Pick's theorem (extended abstract)", editor = "Komei Fukuda and Joris van der Hoeven and Michael Joswig and Nobuki Takayama", booktitle = "Proceedings of ICMS 2010, the Third International Congress on Mathematical Software", address = "Kobe, Japan", date = "September 2010", publisher = "Springer-Verlag", series = "Lecture Notes in Computer Science", volume = 6327, year = 2010, pages = "152--154"}