@article{AM_2000_151_2_a2,
     author = {Joel Hass and Roger Schlafly},
     title = {Double bubbles minimize},
     journal = {Annals of mathematics},
     publisher = {mathdoc},
     volume = {151},
     number = {2},
     year = {2000},
     url = {http://geodesic.mathdoc.fr/item/AM_2000_151_2_a2/}
}