@misc{10_1017_S0008439500030666,
     title = {A {Letter} to {Professor} {J.} {Lambek}},
     journal = {Canadian mathematical bulletin},
     pages = {382--383},
     year = {1969},
     volume = {12},
     number = {3},
     doi = {10.1017/S0008439500030666},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0008439500030666/}
}