## A note on periodic solutions of nonautonomous second-order systems.(English)Zbl 1055.34084

The authors study the multiplicity of periodic solutions for the second-order equation $\ddot u + \nabla F(t,u) = e(t),\quad u\in\mathbb R^n,$ where the function $$F$$ is periodic in the first $$r$$ components of $$u$$ and subquadratically in the other $$n-r$$ components. Using minimax methods, they show that there are at least $$r+1$$ geometrically distinct periodic solutions.
Reviewer: Bin Liu (Beijing)

### MSC:

 34C25 Periodic solutions to ordinary differential equations
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