@article{ELMA_1974__29_141131,
     author = {William A. Webb},
     title = {Rationals {Not} {Expressible} as a {Sum} of {Three} {Unit} {Fractions.}},
     journal = {Elemente der Mathematik},
     pages = {1--6},
     publisher = {mathdoc},
     volume = {29},
     year = {1974},
     zbl = {0272.10012},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1974__29_141131/}
}