%0 Journal Article
%A I. S. Brandt
%T Surfaces of negative extrinsic curvature in a Riemannian space with nonpositive Riemannian curvature
%J Doklady Akademii Nauk
%D 1970
%P 747-749
%V 194
%N 4
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DAN_1970_194_4_a1/
%G ru
%F DAN_1970_194_4_a1