%0 Journal Article
%A L. A. Lepin
%T On the concepts of lower and upper functions
%J Differencialʹnye uravneniâ
%D 1980
%P 1750-1759
%V 16
%N 10
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DE_1980_16_10_a2/
%G ru
%F DE_1980_16_10_a2