@article{10_4153_CMB_1990_072_x,
     author = {Ladas, G.},
     title = {Oscillation in {Differential} {Equations} with {Positive} and {Negative} {Coefficients}},
     journal = {Canadian mathematical bulletin},
     pages = {442--451},
     year = {1990},
     volume = {33},
     number = {4},
     doi = {10.4153/CMB-1990-072-x},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1990-072-x/}
}