@article{ELMA_1968__23_140892,
     author = {F. Harary and D. Cartwright},
     title = {On the {Coloring} of {Signed} {Graphs.}},
     journal = {Elemente der Mathematik},
     pages = {85--89},
     publisher = {mathdoc},
     volume = {23},
     year = {1968},
     zbl = {0155.31703},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1968__23_140892/}
}