@article{CMH_1947__20_138929,
     author = {Hans Georg Haefeli},
     title = {Hyperkomplexe {Differentiale.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {382--420},
     publisher = {mathdoc},
     volume = {20},
     year = {1947},
     zbl = {0035.05801},
     url = {http://geodesic.mathdoc.fr/item/CMH_1947__20_138929/}
}