%0 Journal Article
%A Yu. N. Kiselev
%T Differentiability of a mapping that describes isochrone surfaces in a linear time optimal problem
%J Differencialʹnye uravneniâ
%D 1971
%P 1385-1392
%V 7
%N 8
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DE_1971_7_8_a4/
%G ru
%F DE_1971_7_8_a4