1. O. Axelsson, Solution of linear systems of equations: Iterative methods, in: Sparse Matrix Techniques, Copenhagen 1976 (V. A. Barker, ed.), Springer Verlag, Berlin, 1977, pp. 1–51.
2. D. Braess, Finite Elements. Theory, Fast Solvers, and Applications in Solid Mechanics, Cambridge University Press, Second Edition, 2001.
3. F. Brezzi, On the existence, uniqueness and approximation of saddlepoint problems arising from Lagrangian multipliers, RAIRO Anal. Numér. 8 (1974), 129–151.
4. P. Concus, G. H. Golub, and D. P. O’Leary, A generalized conjugate gradient method for the numerical solution of elliptic partial differential equations, in: Sparse Matrix Computations (J. R. Bunch, D. J. Rose, eds.), Academic Press, New York, 1976.
5. G. H. Golub, C. F. Van Loan, Matrix Computations, The Johns Hopkins University Press, Baltimore, 1996.