@article{MAN_1961__144_160881,
     author = {G.A. DIRAC},
     title = {A contraction theorem for abstract graphs.},
     journal = {Mathematische Annalen},
     pages = {93--96},
     publisher = {mathdoc},
     volume = {144},
     year = {1961},
     zbl = {0107.17301},
     url = {http://geodesic.mathdoc.fr/item/MAN_1961__144_160881/}
}