[1]
L. Sánchez, «A Note on Nontrivial Peniodic Solutions of Dynamical Systems with Subquadratic Potential», Rev. mat. complut., vol. 7, n.º 1, p. 179, ene. 1994, doi: https://doi.org/10.5209/rev_REMA.1994.v7.n1.17799