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This note is an addendum to the results of P.O. Frederickson and A.C. Lazer[1], and A.C. Lazer [4] on periodic oscillations, with linear part atresonance. We show that a small modification of the argument in [4] provides amore general result. It turns out that things are different for thecorresponding Dirichlet boundary value problem.

Harmonic oscillators at resonance, perturbed by a non-linear friction force