@Unpublished{K-theory/0384,
  author = 	 {{Daniel R. Grayson and Mark E. Walker}},
  title = 	 {{Geometric Models for Algebraic K-theory}},
  note = 	 {{Preprint, January 31, 2000, K-theory Preprint Archives, http://www.math.uiuc.edu/K-theory/0384/}}}
}