%0 Journal Article
%A L. N. Shevrin
%T On subsemigroups of free semigroups
%J Doklady Akademii Nauk
%D 1960
%P 537-539
%V 133
%N 3
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DAN_1960_133_3_a9/
%G ru
%F DAN_1960_133_3_a9