@article{03946666, title = {Comparison theorems for fourth order differential equations.}, journal = {International Journal of Mathematics and Mathematical Sciences}, volume = {9}, year = {1986}, pages = {105-109}, doi = {10.1155/S0161171286000133}, zbl = {0589.34028}, language = {en}, url = {http://dml.mathdoc.fr/item/03946666} }
Etgen, Garret J.; Taylor, Willie E.jun. Comparison theorems for fourth order differential equations.. International Journal of Mathematics and Mathematical Sciences, Tome 9 (1986) pp. 105-109. doi : 10.1155/S0161171286000133. http://gdmltest.u-ga.fr/item/03946666/