@article{10_1017_S0017089500003219,
     author = {Chen, Lu-San},
     title = {A {Lyapunov} inequality and forced oscillations in general nonlinear nth order differential-difference equations{\textdagger}},
     journal = {Glasgow mathematical journal},
     pages = {161--166},
     year = {1977},
     volume = {18},
     number = {2},
     doi = {10.1017/S0017089500003219},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500003219/}
}