TY  - JOUR
AU  - S. P. Geisberg
TI  - On the properties of the normal mapping generated by the equations $rt-s^2=-f^2(x,y)$
JO  - Sbornik. Mathematics
PY  - 1970
SP  - 201
EP  - 208
VL  - 11
IS  - 2
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/SM_1970_11_2_a5/
LA  - en
ID  - SM_1970_11_2_a5
ER  -