TY  - JOUR
AU  - H.J. Shyr
TI  - Every subsemigroup of a free semigroup with zero is not an R-semigroup.
JO  - Semigroup forum
PY  - 1976
SP  - 380
EP  - 382
VL  - 12
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/SF_1976__12_134189/
ID  - SF_1976__12_134189
ER  -