@Unpublished{K-theory/0922,
  author = 	 {{Nikita A. Karpenko }},
  title = 	 {{Hyperbolicity of hermitian forms over biquaternion algebras }},
  note = 	 {{Preprint, January 7, 2009, K-theory Preprint Archives, http://www.math.uiuc.edu/K-theory/0922/}}}
}