@article{purd:inex06,
  author	= {William C. Purdy},
  title		= {Inexpressiveness of First-Order Fragments},
  journal	= {The Australasian Journal of Logic},
  year		= 2006,
  volume	= 4,
  pages		= {1-12},
  URL		= {http://www.philosophy.unimelb.edu.au/ajl/2006/},
}