%0 Journal Article
%A V. A. Zalgaller
%A F. L. Litvin
%T A sufficient criterion for the existence of an envelope of characteristics and a~cuspidal edge on the enveloping surface of a~parametrized family of surfaces
%J Izvestiâ vysših učebnyh zavedenij. Matematika
%D 1977
%P 20-23
%N 3
%I mathdoc
%U http://geodesic.mathdoc.fr/item/IVM_1977_3_a2/
%G ru
%F IVM_1977_3_a2