TY  - JOUR
AU  - A. A. Borisenko
TI  - Surfaces of nonpositive extrinsic curvature in spaces of constant curvature
JO  - Sbornik. Mathematics
PY  - 1982
SP  - 297
EP  - 310
VL  - 42
IS  - 3
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/SM_1982_42_3_a0/
LA  - en
ID  - SM_1982_42_3_a0
ER  -