NONLINEAR OSCILLATIONS AT A POINT OF RESONANCE

In this paper, we consider the differential equationd~2x/dt~2+g(x) = p(t),where g(x)∈ C~1(R), p(t)∈C(R) and p(t) is a 2π-periodic function, and resolve rather comptely theproblem of the existence of 2π-periodic solutions for the equation(*) under the assumptious:m~2≤g'(x)≤(m+1)~2,where m is a non-negative integer.