@article{20431,
      author       = "Teunissen, P.J.G. and IUGG XX General Assembly IAG, Vienna,
                      August 11-24, 1991",
      title        = "Nonlinear Adjustment. IAG Special Study Group 4.120. Period
                      1987 - 1991. IUGG General Assembly, Vienna, 11-24 August
                      1991  ",
      year         = "1991",
      note         = "Liter.",
}