TY  - JOUR
AU  - Shiing-Shen Chern
AU  - E. Spanier
TI  - A Theorem on Orientable Surfaces in Four-Dimensional Space.
JO  - Commentarii mathematici Helvetici
PY  - 1951
SP  - 205
EP  - 209
VL  - 25
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/CMH_1951__25_139026/
ID  - CMH_1951__25_139026
ER  -