@article {Boscaggin2013,
	title = {Planar Hamiltonian systems at resonance: the Ahmad{\textendash}Lazer{\textendash}Paul condition},
	journal = {Nonlinear Differential Equations and Applications NoDEA},
	volume = {20},
	number = {3},
	year = {2013},
	month = {Jun},
	pages = {825{\textendash}843},
	abstract = {<p>We consider the planar Hamiltonian system\$\$Ju^{\backslashprime} = \backslashnabla F(u) + \backslashnabla_u R(t,u), \backslashquad t \backslashin [0,T], \backslash,u \backslashin \backslashmathbb{R}^2,\$\$with F(u) positive and positively 2-homogeneous and \$\${\backslashnabla_{u}R(t, u)}\$\$sublinear in u. By means of an Ahmad-Lazer-Paul type condition, we prove the existence of a T-periodic solution when the system is at resonance. The proof exploits a symplectic change of coordinates which transforms the problem into a perturbation of a linear one. The relationship with the Landesman{\textendash}Lazer condition is analyzed, as well.</p>},
	issn = {1420-9004},
	doi = {10.1007/s00030-012-0181-2},
	url = {https://doi.org/10.1007/s00030-012-0181-2},
	author = {Alberto Boscaggin and Maurizio Garrione}
}
