@article{ELMA_1968__23_140886,
     author = {J. Spilker and M.W. Richter},
     title = {Area of the {Union} of {Disks.}},
     journal = {Elemente der Mathematik},
     pages = {60--63},
     publisher = {mathdoc},
     volume = {23},
     year = {1968},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1968__23_140886/}
}