1. S. Banach,Sur les opérations dans les ensembles abstraits et leur application aux équations intégrales, Fund. Math.3 (1922), 133–181.
2. J. B. Diaz and B. Margolis,A fixed point theorem of the alternative for contractions on a generalized complete metric space, Bull. Amer. Math. Soc.,74 (1968), 305–309.
3. M. Edelstein,An extension of Banach’s contraction principle, Proc. Amer. Math. Soc.,12 (1961), 7–10.
4. C. F. K. Jung,On generalized complete metric spaces, Bull. Amer. Math. Soc.,75 (1969), 113–116.
5. W. A. J. Luxemburg,On the convergence of successive approximations in the theory of ordinary differential equations, II, Koninkl. Nederl. Akademie van Wetenschappen, Amsterdam, Proc. Ser.A(5), 61, and Indag. Math. (5), 20 (1958), 540–546.