@article {boscaggin2011subharmonic,
	title = {Subharmonic solutions of planar Hamiltonian systems via the Poincar{\'e}́-Birkhoff theorem},
	journal = {Le Matematiche},
	volume = {66},
	number = {1},
	year = {2011},
	pages = {115{\textendash}122},
	abstract = {<p>We revisit some recent results obtained in [1] about the existence of subharmonic solutions for a class of (nonautonomous) planar Hamiltonian systems, and we compare them with the existing literature. New applications to undamped second order equations are discussed, as well.</p>},
	author = {Alberto Boscaggin}
}
