@article {2021,
	title = {Well-Ordered and Non-Well-Ordered Lower and Upper Solutions for Periodic Planar Systems},
	journal = {Advanced Nonlinear Studies},
	volume = {21},
	year = {2021},
	month = {2021},
	pages = {397 - 419},
	url = {https://doi.org/10.1515/ans-2021-2117},
	author = {Alessandro Fonda and Giuliano Klun and Andrea Sfecci}
}
