TY  - JOUR
AU  - M. M. Lavrent'ev
AU  - V. R. Kireitov
TI  - On branch points of optical hypersurfaces
JO  - Doklady Akademii Nauk
PY  - 1975
SP  - 1027
EP  - 1030
VL  - 221
IS  - 5
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DAN_1975_221_5_a5/
LA  - ru
ID  - DAN_1975_221_5_a5
ER  -