%0 Journal Article
%A T.E. Hall
%A C.J. Ash
%T Invers SEMIGROUPS ON GRAPHS.
%J Semigroup forum
%D 1975
%P 140-145
%V 11
%I mathdoc
%U http://geodesic.mathdoc.fr/item/SF_1975__11_134135/
%F SF_1975__11_134135