TY  - JOUR
TI  - Letter
JO  - Canadian mathematical bulletin
PY  - 1962
SP  - 91
EP  - 92
VL  - 5
IS  - 1
UR  - http://geodesic.mathdoc.fr/articles/10.1017/S0008439500026060/
DO  - 10.1017/S0008439500026060
ID  - 10_1017_S0008439500026060
ER  -