TY  - JOUR
AU  - Shi Mingquan
TI  - π1-Semigroup
JO  - Mathematica balkanica
PY  - 1991
SP  - 203
VL  - 5
IS  - 3
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/MABA_1991_5_3_a3/
ID  - MABA_1991_5_3_a3
ER  -