1. M. Furi -M. Martelli -A. Vignoli,On the solvability of nonlinear operator equations in normed spaces, Ann. Mat. Pura Appl.,124 (1980), pp. 321–343.
2. M. Furi -M. P. Pera,On the existence of an unbounded connected set of solutions for non-linear equations in Banach spaces, Atti Accad. Naz. Lincei, Rend. Cl. Sc. Mat. Fis. Nat.,67 (1979), pp. 31–38.
3. M. Furi -M. P. Pera,An elementary approach to boundary value problems at resonance, Nonlinear Analysis, Theory, Methods, Appl.,4 (1980), pp. 1081–1089.
4. M. Furi -M. P. Pera,Nonbifurcating branches of forced oscillations for the differential systemx(t=λf(t, x(t)), λ⩾0, Boll. Un. Mat. Ital., sez. C. Serie VI,2-C (1983), pp. 187–194.
5. C. Kuratowski,Topology, vol. 2, Academic Press, New York, 1968.