@article{10_4153_CMB_2010_030_4,
     author = {Papageorgiou, Nikolaos S. and Staicu, Vasile},
     title = {Multiple {Nontrivial} {Solutions} for {Doubly} {Resonant} {Periodic} {Problems}},
     journal = {Canadian mathematical bulletin},
     pages = {347--359},
     year = {2010},
     volume = {53},
     number = {2},
     doi = {10.4153/CMB-2010-030-4},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-2010-030-4/}
}