@article{JRAM_1965__218_150684,
     author = {E. Stiefel and P. Kustaanheimo},
     title = {Perturbation theory of {Kepler} motion based on spinor regularization.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {204--219},
     publisher = {mathdoc},
     volume = {218},
     year = {1965},
     zbl = {0151.34901},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1965__218_150684/}
}