TY  - JOUR
AU  - Joachim A. Hempel
TI  - A pseudo-trigonometry related to Ptolemy's theorem
 and the hyperbolic geometry of punctured spheres
JO  - Annales Polonici Mathematici
PY  - 2004
SP  - 147
EP  - 167
VL  - 84
IS  - 2
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/articles/10.4064/ap84-2-5/
DO  - 10.4064/ap84-2-5
LA  - en
ID  - 10_4064_ap84_2_5
ER  -