1. Athanassov Z.S.,Uniqueness and convergence of succesive approximations for ordinary differential equations, Math. Japonica35 (1990) 351–367.
2. Conti R., Sansone G.,Equazioni differenziali non lineari, Monografie Matematiche del C.N.R., Roma 1956.
3. Wintner A.,On the local uniqueness of the initial value problem for the differential equation d nx/dtn=f(t, x), Boll. Un. Mat. Ital.11 (1956), 496–498.