@article{MZ_1965__88_170407,
     author = {K. Varadarajan},
     title = {On fibrations and category.},
     journal = {Mathematische Zeitschrift},
     pages = {267--273},
     year = {1965},
     volume = {88},
     zbl = {0163.17905},
     url = {http://geodesic.mathdoc.fr/item/MZ_1965__88_170407/}
}