@article {boscaggin2011subharmonic,
	title = {Subharmonic solutions of planar Hamiltonian systems: a rotation number approach},
	journal = {Advanced Nonlinear Studies},
	volume = {11},
	number = {1},
	year = {2011},
	pages = {77{\textendash}103},
	publisher = {Advanced Nonlinear Studies, Inc.},
	doi = {10.1515/ans-2011-0104},
	author = {Alberto Boscaggin}
}
