%0 Journal Article
%A P.C. Trotter
%T On a problem of Pastijn and Petrich.
%J Semigroup forum
%D 1986
%P 249-252
%V 34
%I mathdoc
%U http://geodesic.mathdoc.fr/item/SF_1986__34_134843/
%F SF_1986__34_134843