Existence of nonnegative solutions are established for the periodic problem $y'=f(t,y)$ a.e\. on $[0,T]$, $y(0)=y(T)$. Here the nonlinearity $f$ satisfies a Landesman Lazer type condition.
@article{118928, author = {Donal O'Regan}, title = {Landesman Lazer type results for first order periodic problems}, journal = {Commentationes Mathematicae Universitatis Carolinae}, volume = {38}, year = {1997}, pages = {297-308}, zbl = {0893.34012}, mrnumber = {1455497}, language = {en}, url = {http://dml.mathdoc.fr/item/118928} }
O'Regan, Donal. Landesman Lazer type results for first order periodic problems. Commentationes Mathematicae Universitatis Carolinae, Tome 38 (1997) pp. 297-308. http://gdmltest.u-ga.fr/item/118928/
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