@article{AFM_1977_3_2_a14,
     author = {Douglas M. Campbell and Gene H. Wickes},
     title = {The spherical derivative and normal functions {(II)}},
     journal = {Annales Fennici Mathematici},
     pages = {373--375},
     year = {1977},
     volume = {3},
     number = {2},
     doi = {10.5186/aasfm.1977.0302},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.5186/aasfm.1977.0302/}
}