The double bubble conjecture. Hass, Joel; Hutchings, Michael; Schlafly, Roger — 1995 Electronic Research Announcements of the American Mathematical Society [electronic only]
Surface Minimizing Area in Their Homology Class and Group Actions on 3-Manifolds. Joel Hass — 1988 Mathematische Zeitschrift
Unstable minimal surfaces and Heegaard splittings. Joel Hass; Charles Frohman — 1989 Inventiones mathematicae
Homotopy and isotopy in dimension three. Joel Hass; Peter Scott — 1993 Commentarii mathematici Helvetici