On the solvability of semilinear elliptic equation via an associated eigenvaule problem. Gabriella Tarantello; Stanley Alama — 1996 Mathematische Zeitschrift
Solutions of elliptic equations with indefinite nonlinearities via Morse theory and linking Stanley Alama; Manuel Del Pino — 1996 Annales de l'I.H.P. Analyse non linéaire