@article{JRAM_1971__248_151114,
     author = {Azmi Hanna},
     title = {On the homology theory of categories. {I.}},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {133--146},
     publisher = {mathdoc},
     volume = {248},
     year = {1971},
     zbl = {0288.18009},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1971__248_151114/}
}