[2] P. Läuchli: Jordan-Elimination und Ausgleichung nach kleinsten Quadraten. Numer. Math., Vol. 3 (1961), pp. 226-240. DOI 10.1007/BF01386022 | MR 0135225
[3] У. Linnik: Method of Least Squares and Principles of the Theory of Observations. translated from Russian by R. C. Elandt, Pergamon Press, New York, 1961. MR 0124121 | Zbl 0112.11105