@article{10_4064_ap_21_2_175_194,
     author = {D. Willett},
     title = {On the oscillatory behavior of the solutions of second order linear differential equations},
     journal = {Annales Polonici Mathematici},
     pages = {175--194},
     year = {1968},
     volume = {21},
     number = {2},
     doi = {10.4064/ap-21-2-175-194},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-21-2-175-194/}
}