TY  - JOUR
AU  - Peter Lappan
TI  - The spherical derivative and normal functions
JO  - Annales Fennici Mathematici
PY  - 1977
SP  - 301
EP  - 310
VL  - 3
IS  - 2
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/articles/10.5186/aasfm.1977.0312/
DO  - 10.5186/aasfm.1977.0312
LA  - en
ID  - AFM_1977_3_2_a9
ER  -