%0 Journal Article
%A M. M. Lavrent'ev
%A V. R. Kireitov
%T On branch points of optical hypersurfaces
%J Doklady Akademii Nauk
%D 1975
%P 1027-1030
%V 221
%N 5
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DAN_1975_221_5_a5/
%G ru
%F DAN_1975_221_5_a5