%0 Journal Article
%A R. F. Polishchuk
%T On the classification of the curvature tensor by means of principal congruences
%J Doklady Akademii Nauk
%D 1970
%P 62-65
%V 194
%N 1
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DAN_1970_194_1_a15/
%G ru
%F DAN_1970_194_1_a15