On bounded solutions of ordinary nonlinear differential equations of order n

To prove the existence and uniqueness (or only the existence) of a bounded solution of a weakly nonlinear differential equation of the nth order, we use both the contraction mapping principle and the Tikhonov fixed-point theorem. We obtain an important qualitative estimate for the smallness of a nonlinear perturbation preserving the basic characteristics of the behavior of a linear equation (absolute stability or exponential dichotomy) under the passage to the nonlinear equation.