@article{MAN_1970__190_162102,
     author = {G.M. RINGEL},
     title = {Faserungen und {Homotopie} in {Kategorien.}},
     journal = {Mathematische Annalen},
     pages = {215--230},
     publisher = {mathdoc},
     volume = {190},
     year = {1970},
     url = {http://geodesic.mathdoc.fr/item/MAN_1970__190_162102/}
}