Variational and Topological Methods in Partially Ordered Hilbert Spaces. Helmut Hofer — 1982 Mathematische Annalen
Lagrangian embeddings and critical point theory Helmut Hofer — 1985 Annales de l'I.H.P. Analyse non linéaire
Symplectic Topology and Hamiltonian Dynamics II. Helmut Hofer; Ivar Ekeland — 1990 Mathematische Zeitschrift
Homoclinic, Heteroclinic, and Periodic Orbits for a Class of Indefinite Hamiltonian Systems. Helmut Hofer; John Toland — 1984 Mathematische Annalen
A general Fredholm theory I: a splicing-based differential geometry Helmut Hofer; Kris Wysocki; Eduard Zehnder — 2007 Journal of the European Mathematical Society