@article{10_4064_ap_42_1_159_164,
     author = {V. Lakshmikantham and S. Leela},
     title = {On the method of upper and lower solutions in abstract cones},
     journal = {Annales Polonici Mathematici},
     pages = {159--164},
     publisher = {mathdoc},
     volume = {42},
     number = {1},
     year = {1983},
     doi = {10.4064/ap-42-1-159-164},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-42-1-159-164/}
}