@article{EJDE_2009__2009__a77,
     author = {Kwong,  Man Kam and Wong,  James S.W.},
     title = {An optimal existence theorem for positive solutions of a four-point boundary value problem},
     journal = {Electronic journal of differential equations},
     year = {2009},
     volume = {2009},
     zbl = {1193.34033},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2009__2009__a77/}
}