@misc{10_1017_S0008439500026060,
     title = {Letter},
     journal = {Canadian mathematical bulletin},
     pages = {91--92},
     year = {1962},
     volume = {5},
     number = {1},
     doi = {10.1017/S0008439500026060},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0008439500026060/}
}