A second look at the first result of Landesman-Lazer type. Lazer, Alan C. — 2000 Electronic Journal of Differential Equations (EJDE) [electronic only]
Homoclinic orbits for a class of symmetric Hamiltonian systems. Korman, Philip; Lazer, Alan C. — 1994 Electronic Journal of Differential Equations (EJDE) [electronic only]
On the asymptotic behavior of solutions of the differential equation y ( 4 ) = p ( t ) y Stuart P. Hastings; Alan C. Lazer — 1968 Czechoslovak Mathematical Journal