TY  - JOUR
AU  - Goebel, K.
TI  - Convexity of balls and fixed-point theorems for mappings with nonexpansive square
JO  - Compositio Mathematica
PY  - 1970
SP  - 269
EP  - 274
VL  - 22
IS  - 3
PB  - Wolters-Noordhoff Publishing
UR  - http://www.numdam.org/item/CM_1970__22_3_269_0/
LA  - en
ID  - CM_1970__22_3_269_0
ER  -