@article{10_4153_CJM_1975_017_4,
     author = {Lewis, Roger T.},
     title = {The {Oscillation} of {Fourth} {Order} {Linear} {Differential} {Operators}},
     journal = {Canadian journal of mathematics},
     pages = {138--145},
     year = {1975},
     volume = {27},
     number = {1},
     doi = {10.4153/CJM-1975-017-4},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1975-017-4/}
}