John J. Buoni and Richard S. Varga, Theorems of Stein-Rosenberg Type, Numerical Mathematics (R. Ansorge, K. Glasho , B. Werner, eds.), pp. 65-75, ISNM 49, Birkh� auser Verlag, Basel, 1979. MR 83b:65028. Zbl. 412.65016.