@Article{HA99,
  author = 	 {W. Hackbusch},
  title = 	 {A sparse matrix arithmetic based on $\mathcal{H}$-Matrices. {P}art {I}: {I}ntroduction to $\mathcal{H}$-Matrices},
  journal = 	 {Computing},
  year = 	 {1999},
  volume = 	 {62},
  pages = 	 {89--108}
}

@InProceedings{HAKHSA00,
  author = 	 {W. Hackbusch and B.~N. Khoromskij and S.~A. Sauter},
  title = 	 {On $\mathcal{H}^2$-Matrices},
  booktitle = 	 {Lectures on Applied Mathematics},
  editor = 	 {H. Bungartz and R. Hoppe and C. Zenger},
  publisher =    {Springer-Verlag, Berlin},
  year = 	 {2000},
  pages = 	 {9--29}
}

@Article{BOHA02,
  author = 	 {S. {B\"orm} and W. Hackbusch},
  title = 	 {Data-sparse approximation by adaptive {${\mathcal{H}}^2$}-matrices},
  journal = 	 {Computing},
  year = 	 {2002},
  volume = 	 {69},
  pages = 	 {1--35},
  preprint =     {86/2001}
}

@Article{GRHA02,
  author = 	 {L. Grasedyck and W. Hackbusch},
  title = 	 {Construction and arithmetics of {${\mathcal{H}}$}-matrices},
  journal = 	 {Computing},
  year = 	 {2003},
  volume = 	 {70},
  pages = 	 {295--334}
}

@Book{HA09,
  author = 	 {W. Hackbusch},
  title = 	 {{Hierarchische} {Matrizen} --- {Algorithmen} und {Analysis}},
  publisher = 	 {Springer},
  year = 	 {2009}
}

@Book{BO10,
  author = 	 {S. {B\"orm}},
  title = 	 {Efficient Numerical Methods for Non-local Operators: {${\mathcal H}^2$}-Matrix Compression, Algorithms and Analysis},
  publisher = 	 {EMS},
  year = 	 {2010},
  volume = 	 {14},
  series = 	 {EMS Tracts in Mathematics}
}