@article{10_2307_121042,
     author = {Joel Hass and Roger Schlafly},
     title = {Double bubbles minimize},
     journal = {Annals of mathematics},
     year = {2000},
     volume = {151},
     number = {2},
     doi = {10.2307/121042},
     zbl = {0970.53008},
     url = {http://geodesic.mathdoc.fr/articles/10.2307/121042/}
}