1. Hubbard (ed.), Numerical Solution of PDE-II, Academic Press 1971.Especially the papers by Babuška; Bramble and Schatz; Marcal; Strang; and references therein.
2. E. Wachspres, Iterative solutions of Elliptic Systems, Prentice Hall, 1966.
3. P. P. Fedorenko, Zh.
$$v\bar ychisl.$$
Mat. Fiz. 4,3 (1964), 559–664.
4. N. S. Bakhvalov, Zh.
$$v\bar ychisl.$$
Mat. Fiz. 6,5 (1966), 861–885.
5. H. L. Stone, SIAM J. Num. Anal., 5 (1968), 530–558.