%0 Journal Article
%A S. P. Geisberg
%T On the properties of the normal mapping generated by the equations $rt-s^2=-f^2(x,y)$
%J Sbornik. Mathematics
%D 1970
%P 201-208
%V 11
%N 2
%I mathdoc
%U http://geodesic.mathdoc.fr/item/SM_1970_11_2_a5/
%G en
%F SM_1970_11_2_a5